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 $224.93   12.451%   $252.936   $252.94   $252.95   $252.90  
  Purchase #2 $122.26   8.515%   $132.6704   $132.67   $132.65   $132.70  
  Purchase #3 $40.89   7.814%   $44.0851   $44.09   $44.10   $44.10  
  Purchase #4 $246.64   13.660%   $280.331   $280.33   $280.35   $280.30  
  Purchase #5 $117.57   4.597%   $122.9747   $122.97   $122.95   $123.00  
  Purchase #6 $188.50   4.800%   $197.548   $197.55   $197.55   $197.50  
  Purchase #7 $5.95   3.422%   $6.1536   $6.15   $6.15   $6.20  
  7 purchase totals = $946.74       $1,036.6988   $1,036.70   $1,036.70   $1,036.70