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 $195.67   8.858%   $213.0024   $213.00   $213.00   $213.00  
  Purchase #2 $48.76   6.158%   $51.7626   $51.76   $51.75   $51.80  
  Purchase #3 $66.87   12.439%   $75.188   $75.19   $75.20   $75.20  
  Purchase #4 $64.28   5.643%   $67.9073   $67.91   $67.90   $67.90  
  Purchase #5 $221.51   7.263%   $237.5983   $237.60   $237.60   $237.60  
  Purchase #6 $167.32   3.574%   $173.3   $173.30   $173.30   $173.30  
  Purchase #7 $31.62   3.204%   $32.6331   $32.63   $32.65   $32.60  
  7 purchase totals = $796.03       $851.3917   $851.39   $851.40   $851.40