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 $183.85   11.507%   $205.0056   $205.01   $205.00   $205.00  
  Purchase #2 $96.71   11.455%   $107.7881   $107.79   $107.80   $107.80  
  Purchase #3 $52.56   3.604%   $54.4543   $54.45   $54.45   $54.50  
  Purchase #4 $101.58   13.694%   $115.4904   $115.49   $115.50   $115.50  
  Purchase #5 $201.51   7.125%   $215.8676   $215.87   $215.85   $215.90  
  Purchase #6 $180.68   5.439%   $190.5072   $190.51   $190.50   $190.50  
  Purchase #7 $119.36   10.532%   $131.931   $131.93   $131.95   $131.90  
  7 purchase totals = $936.25       $1,021.0442   $1,021.05   $1,021.05   $1,021.10