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 $60.45   12.504%   $68.0087   $68.01   $68.00   $68.00  
  Purchase #2 $118.84   9.519%   $130.1524   $130.15   $130.15   $130.20  
  Purchase #3 $187.38   7.666%   $201.7446   $201.74   $201.75   $201.70  
  Purchase #4 $77.99   8.237%   $84.414   $84.41   $84.40   $84.40  
  Purchase #5 $189.55   10.149%   $208.7874   $208.79   $208.80   $208.80  
  Purchase #6 $12.64   5.449%   $13.3288   $13.33   $13.35   $13.30  
  Purchase #7 $73.29   3.791%   $76.0684   $76.07   $76.05   $76.10  
  7 purchase totals = $720.14       $782.5043   $782.50   $782.50   $782.50