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 $88.74   11.285%   $98.7543   $98.75   $98.75   $98.80  
  Purchase #2 $191.75   8.600%   $208.2405   $208.24   $208.25   $208.20  
  Purchase #3 $98.86   9.763%   $108.5117   $108.51   $108.50   $108.50  
  Purchase #4 $48.85   6.806%   $52.1747   $52.17   $52.15   $52.20  
  Purchase #5 $194.67   6.224%   $206.7863   $206.79   $206.80   $206.80  
  Purchase #6 $68.61   5.219%   $72.1908   $72.19   $72.20   $72.20  
  Purchase #7 $11.84   6.137%   $12.5666   $12.57   $12.55   $12.60  
  7 purchase totals = $703.32       $759.2249   $759.22   $759.20   $759.30