Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.86   13.414%   $235.7423   $235.74   $235.75   $235.70  
  Purchase #2 $205.69   12.395%   $231.1853   $231.19   $231.20   $231.20  
  Purchase #3 $227.95   10.296%   $251.4197   $251.42   $251.40   $251.40  
  Purchase #4 $226.30   6.514%   $241.0412   $241.04   $241.05   $241.00  
  Purchase #5 $215.95   13.635%   $245.3948   $245.39   $245.40   $245.40  
  Purchase #6 $245.99   11.366%   $273.9492   $273.95   $273.95   $273.90  
  Purchase #7 $114.51   3.251%   $118.2327   $118.23   $118.25   $118.20  
  7 purchase totals = $1,444.25       $1,596.9652   $1,596.96   $1,597.00   $1,596.80