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 $76.66   11.172%   $85.2245   $85.22   $85.20   $85.20  
  Purchase #2 $155.56   9.506%   $170.3475   $170.35   $170.35   $170.30  
  Purchase #3 $125.90   5.864%   $133.2828   $133.28   $133.30   $133.30  
  Purchase #4 $100.31   9.315%   $109.6539   $109.65   $109.65   $109.70  
  Purchase #5 $169.89   3.217%   $175.3554   $175.36   $175.35   $175.40  
  Purchase #6 $25.56   6.468%   $27.2132   $27.21   $27.20   $27.20  
  Purchase #7 $250.91   6.248%   $266.5869   $266.59   $266.60   $266.60  
  7 purchase totals = $904.79       $967.6642   $967.66   $967.65   $967.70