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 $201.54   3.193%   $207.9752   $207.98   $208.00   $208.00  
  Purchase #2 $150.36   10.482%   $166.1207   $166.12   $166.10   $166.10  
  Purchase #3 $45.53   11.838%   $50.9198   $50.92   $50.90   $50.90  
  Purchase #4 $34.62   5.506%   $36.5262   $36.53   $36.55   $36.50  
  Purchase #5 $62.76   9.819%   $68.9224   $68.92   $68.90   $68.90  
  Purchase #6 $175.26   6.808%   $187.1917   $187.19   $187.20   $187.20  
  Purchase #7 $240.41   11.804%   $268.788   $268.79   $268.80   $268.80  
  7 purchase totals = $910.48       $986.4440   $986.45   $986.45   $986.40