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 $46.51   13.863%   $52.9577   $52.96   $52.95   $53.00  
  Purchase #2 $198.46   9.152%   $216.6231   $216.62   $216.60   $216.60  
  Purchase #3 $12.70   13.114%   $14.3655   $14.37   $14.35   $14.40  
  Purchase #4 $208.71   4.394%   $217.8807   $217.88   $217.90   $217.90  
  Purchase #5 $107.89   9.122%   $117.7317   $117.73   $117.75   $117.70  
  Purchase #6 $208.40   10.505%   $230.2924   $230.29   $230.30   $230.30  
  Purchase #7 $82.59   7.326%   $88.6405   $88.64   $88.65   $88.60  
  7 purchase totals = $865.26       $938.4916   $938.49   $938.50   $938.50