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 $95.39   7.421%   $102.4689   $102.47   $102.45   $102.50  
  Purchase #2 $103.31   7.407%   $110.9622   $110.96   $110.95   $111.00  
  Purchase #3 $114.81   10.215%   $126.5378   $126.54   $126.55   $126.50  
  Purchase #4 $194.62   5.447%   $205.221   $205.22   $205.20   $205.20  
  Purchase #5 $116.40   13.854%   $132.5261   $132.53   $132.55   $132.50  
  Purchase #6 $56.66   4.494%   $59.2063   $59.21   $59.20   $59.20  
  Purchase #7 $193.45   12.219%   $217.0877   $217.09   $217.10   $217.10  
  7 purchase totals = $874.64       $954.0100   $954.02   $954.00   $954.00