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 $54.73   12.454%   $61.5461   $61.55   $61.55   $61.50  
  Purchase #2 $191.62   5.807%   $202.7474   $202.75   $202.75   $202.70  
  Purchase #3 $157.72   7.161%   $169.0143   $169.01   $169.00   $169.00  
  Purchase #4 $58.91   11.155%   $65.4814   $65.48   $65.50   $65.50  
  Purchase #5 $49.71   9.271%   $54.3186   $54.32   $54.30   $54.30  
  Purchase #6 $78.96   12.442%   $88.7842   $88.78   $88.80   $88.80  
  Purchase #7 $226.77   12.533%   $255.1911   $255.19   $255.20   $255.20  
  7 purchase totals = $818.42       $897.0831   $897.08   $897.10   $897.00