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 $214.78   9.560%   $235.313   $235.31   $235.30   $235.30  
  Purchase #2 $186.76   5.627%   $197.269   $197.27   $197.25   $197.30  
  Purchase #3 $82.79   10.143%   $91.1874   $91.19   $91.20   $91.20  
  Purchase #4 $190.45   12.389%   $214.0449   $214.04   $214.05   $214.00  
  Purchase #5 $18.73   6.792%   $20.0021   $20.00   $20.00   $20.00  
  Purchase #6 $138.72   11.816%   $155.1112   $155.11   $155.10   $155.10  
  Purchase #7 $224.55   13.202%   $254.1951   $254.20   $254.20   $254.20  
  7 purchase totals = $1,056.78       $1,167.1227   $1,167.12   $1,167.10   $1,167.10