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 $41.52   3.421%   $42.9404   $42.94   $42.95   $42.90  
  Purchase #2 $167.62   11.549%   $186.9784   $186.98   $187.00   $187.00  
  Purchase #3 $244.94   13.414%   $277.7963   $277.80   $277.80   $277.80  
  Purchase #4 $23.35   11.105%   $25.943   $25.94   $25.95   $25.90  
  Purchase #5 $172.64   3.228%   $178.2128   $178.21   $178.20   $178.20  
  Purchase #6 $18.84   8.335%   $20.4103   $20.41   $20.40   $20.40  
  Purchase #7 $229.95   12.767%   $259.3077   $259.31   $259.30   $259.30  
  7 purchase totals = $898.86       $991.5889   $991.59   $991.60   $991.50