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 $91.95   13.357%   $104.2318   $104.23   $104.25   $104.20  
  Purchase #2 $143.70   11.840%   $160.7141   $160.71   $160.70   $160.70  
  Purchase #3 $92.36   7.236%   $99.0432   $99.04   $99.05   $99.00  
  Purchase #4 $60.88   8.397%   $65.9921   $65.99   $66.00   $66.00  
  Purchase #5 $250.71   10.200%   $276.2824   $276.28   $276.30   $276.30  
  Purchase #6 $237.98   10.664%   $263.3582   $263.36   $263.35   $263.40  
  Purchase #7 $77.85   9.749%   $85.4396   $85.44   $85.45   $85.40  
  7 purchase totals = $955.43       $1,055.0614   $1,055.05   $1,055.10   $1,055.00