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 $66.54   13.502%   $75.5242   $75.52   $75.50   $75.50  
  Purchase #2 $188.72   5.538%   $199.1713   $199.17   $199.15   $199.20  
  Purchase #3 $130.47   8.727%   $141.8561   $141.86   $141.85   $141.90  
  Purchase #4 $174.73   10.661%   $193.358   $193.36   $193.35   $193.40  
  Purchase #5 $26.36   10.311%   $29.078   $29.08   $29.10   $29.10  
  Purchase #6 $115.38   5.438%   $121.6544   $121.65   $121.65   $121.70  
  Purchase #7 $66.80   10.104%   $73.5495   $73.55   $73.55   $73.50  
  7 purchase totals = $769.00       $834.1915   $834.19   $834.15   $834.30