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 $150.83   12.862%   $170.2298   $170.23   $170.25   $170.20  
  Purchase #2 $173.93   12.391%   $195.4817   $195.48   $195.50   $195.50  
  Purchase #3 $101.82   12.834%   $114.8876   $114.89   $114.90   $114.90  
  Purchase #4 $44.77   3.493%   $46.3338   $46.33   $46.35   $46.30  
  Purchase #5 $152.62   9.444%   $167.0334   $167.03   $167.05   $167.00  
  Purchase #6 $134.81   13.307%   $152.7492   $152.75   $152.75   $152.70  
  Purchase #7 $216.66   4.567%   $226.5549   $226.55   $226.55   $226.60  
  7 purchase totals = $975.44       $1,073.2704   $1,073.26   $1,073.35   $1,073.20