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 $201.83   7.641%   $217.2518   $217.25   $217.25   $217.30  
  Purchase #2 $76.46   7.285%   $82.0301   $82.03   $82.05   $82.00  
  Purchase #3 $157.41   4.863%   $165.0648   $165.06   $165.05   $165.10  
  Purchase #4 $191.45   3.245%   $197.6626   $197.66   $197.65   $197.70  
  Purchase #5 $83.52   11.850%   $93.4171   $93.42   $93.40   $93.40  
  Purchase #6 $91.40   13.780%   $103.9949   $103.99   $104.00   $104.00  
  Purchase #7 $64.36   12.682%   $72.5221   $72.52   $72.50   $72.50  
  7 purchase totals = $866.43       $931.9434   $931.93   $931.90   $932.00