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 $68.28   13.790%   $77.6958   $77.70   $77.70   $77.70  
  Purchase #2 $238.80   13.720%   $271.5634   $271.56   $271.55   $271.60  
  Purchase #3 $20.33   13.849%   $23.1455   $23.15   $23.15   $23.10  
  Purchase #4 $150.65   12.441%   $169.3924   $169.39   $169.40   $169.40  
  Purchase #5 $131.77   3.319%   $136.1434   $136.14   $136.15   $136.10  
  Purchase #6 $30.80   4.507%   $32.1882   $32.19   $32.20   $32.20  
  Purchase #7 $234.97   3.589%   $243.4031   $243.40   $243.40   $243.40  
  7 purchase totals = $875.60       $953.5318   $953.53   $953.55   $953.50