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 $105.61   7.812%   $113.8603   $113.86   $113.85   $113.90  
  Purchase #2 $25.89   3.364%   $26.7609   $26.76   $26.75   $26.80  
  Purchase #3 $135.34   10.600%   $149.686   $149.69   $149.70   $149.70  
  Purchase #4 $149.84   13.445%   $169.986   $169.99   $170.00   $170.00  
  Purchase #5 $240.45   13.110%   $271.973   $271.97   $271.95   $272.00  
  Purchase #6 $12.93   10.758%   $14.321   $14.32   $14.30   $14.30  
  Purchase #7 $125.81   9.634%   $137.9305   $137.93   $137.95   $137.90  
  7 purchase totals = $795.87       $884.5177   $884.52   $884.50   $884.60