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 $48.36   13.630%   $54.9515   $54.95   $54.95   $55.00  
  Purchase #2 $110.36   10.299%   $121.726   $121.73   $121.75   $121.70  
  Purchase #3 $195.88   5.285%   $206.2323   $206.23   $206.25   $206.20  
  Purchase #4 $91.60   11.220%   $101.8775   $101.88   $101.90   $101.90  
  Purchase #5 $184.62   10.483%   $203.9737   $203.97   $203.95   $204.00  
  Purchase #6 $83.26   5.858%   $88.1374   $88.14   $88.15   $88.10  
  Purchase #7 $49.55   6.164%   $52.6043   $52.60   $52.60   $52.60  
  7 purchase totals = $763.63       $829.5027   $829.50   $829.55   $829.50