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 $112.95   11.575%   $126.024   $126.02   $126.00   $126.00  
  Purchase #2 $64.85   10.872%   $71.9005   $71.90   $71.90   $71.90  
  Purchase #3 $97.60   9.562%   $106.9325   $106.93   $106.95   $106.90  
  Purchase #4 $102.78   10.309%   $113.3756   $113.38   $113.40   $113.40  
  Purchase #5 $172.43   7.790%   $185.8623   $185.86   $185.85   $185.90  
  Purchase #6 $74.52   9.156%   $81.3431   $81.34   $81.35   $81.30  
  Purchase #7 $121.84   12.639%   $137.2394   $137.24   $137.25   $137.20  
  7 purchase totals = $746.97       $822.6774   $822.67   $822.70   $822.60