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 $56.55   12.745%   $63.7573   $63.76   $63.75   $63.80  
  Purchase #2 $231.73   8.402%   $251.2   $251.20   $251.20   $251.20  
  Purchase #3 $107.68   10.676%   $119.1759   $119.18   $119.20   $119.20  
  Purchase #4 $203.60   6.782%   $217.4082   $217.41   $217.40   $217.40  
  Purchase #5 $206.75   9.344%   $226.0687   $226.07   $226.05   $226.10  
  Purchase #6 $189.75   10.316%   $209.3246   $209.32   $209.30   $209.30  
  Purchase #7 $240.93   10.268%   $265.6687   $265.67   $265.65   $265.70  
  7 purchase totals = $1,236.99       $1,352.6034   $1,352.61   $1,352.55   $1,352.70