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 $84.60   12.818%   $95.444   $95.44   $95.45   $95.40  
  Purchase #2 $12.61   5.147%   $13.259   $13.26   $13.25   $13.30  
  Purchase #3 $224.60   4.268%   $234.1859   $234.19   $234.20   $234.20  
  Purchase #4 $61.74   11.352%   $68.7487   $68.75   $68.75   $68.70  
  Purchase #5 $153.96   7.816%   $165.9935   $165.99   $166.00   $166.00  
  Purchase #6 $187.54   7.468%   $201.5455   $201.55   $201.55   $201.50  
  Purchase #7 $192.89   11.486%   $215.0453   $215.05   $215.05   $215.00  
  7 purchase totals = $917.94       $994.2219   $994.23   $994.25   $994.10