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 $201.36   5.582%   $212.5999   $212.60   $212.60   $212.60  
  Purchase #2 $67.76   7.655%   $72.947   $72.95   $72.95   $72.90  
  Purchase #3 $37.71   4.500%   $39.407   $39.41   $39.40   $39.40  
  Purchase #4 $154.65   3.673%   $160.3303   $160.33   $160.35   $160.30  
  Purchase #5 $111.30   10.147%   $122.5936   $122.59   $122.60   $122.60  
  Purchase #6 $201.69   11.374%   $224.6302   $224.63   $224.65   $224.60  
  Purchase #7 $92.63   10.115%   $101.9995   $102.00   $102.00   $102.00  
  7 purchase totals = $867.10       $934.5075   $934.51   $934.55   $934.40