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 $155.48   11.676%   $173.6338   $173.63   $173.65   $173.60  
  Purchase #2 $181.93   10.751%   $201.4893   $201.49   $201.50   $201.50  
  Purchase #3 $59.82   12.215%   $67.127   $67.13   $67.15   $67.10  
  Purchase #4 $67.58   10.186%   $74.4637   $74.46   $74.45   $74.50  
  Purchase #5 $244.99   6.136%   $260.0226   $260.02   $260.00   $260.00  
  Purchase #6 $136.63   3.635%   $141.5965   $141.60   $141.60   $141.60  
  Purchase #7 $29.99   10.742%   $33.2115   $33.21   $33.20   $33.20  
  7 purchase totals = $876.42       $951.5444   $951.54   $951.55   $951.50