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 $24.34   9.676%   $26.6951   $26.70   $26.70   $26.70  
  Purchase #2 $207.72   4.494%   $217.0549   $217.05   $217.05   $217.10  
  Purchase #3 $69.30   9.695%   $76.0186   $76.02   $76.00   $76.00  
  Purchase #4 $150.57   12.843%   $169.9077   $169.91   $169.90   $169.90  
  Purchase #5 $154.50   12.244%   $173.417   $173.42   $173.40   $173.40  
  Purchase #6 $220.88   8.455%   $239.5554   $239.56   $239.55   $239.60  
  Purchase #7 $34.41   11.351%   $38.3159   $38.32   $38.30   $38.30  
  7 purchase totals = $861.72       $940.9646   $940.98   $940.90   $941.00