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 $61.29   7.634%   $65.9689   $65.97   $65.95   $66.00  
  Purchase #2 $233.75   9.281%   $255.4443   $255.44   $255.45   $255.40  
  Purchase #3 $116.87   7.483%   $125.6154   $125.62   $125.60   $125.60  
  Purchase #4 $249.52   6.102%   $264.7457   $264.75   $264.75   $264.70  
  Purchase #5 $6.49   13.758%   $7.3829   $7.38   $7.40   $7.40  
  Purchase #6 $50.49   4.191%   $52.606   $52.61   $52.60   $52.60  
  Purchase #7 $215.67   5.271%   $227.038   $227.04   $227.05   $227.00  
  7 purchase totals = $934.08       $998.8012   $998.81   $998.80   $998.70