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 $181.41   11.433%   $202.1506   $202.15   $202.15   $202.20  
  Purchase #2 $68.41   13.637%   $77.7391   $77.74   $77.75   $77.70  
  Purchase #3 $142.29   10.350%   $157.017   $157.02   $157.00   $157.00  
  Purchase #4 $46.59   13.638%   $52.9439   $52.94   $52.95   $52.90  
  Purchase #5 $210.27   3.192%   $216.9818   $216.98   $217.00   $217.00  
  Purchase #6 $18.96   5.301%   $19.9651   $19.97   $19.95   $20.00  
  Purchase #7 $215.85   5.189%   $227.0505   $227.05   $227.05   $227.10  
  7 purchase totals = $883.78       $953.8480   $953.85   $953.85   $953.90