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 $228.98   8.571%   $248.6059   $248.61   $248.60   $248.60  
  Purchase #2 $59.38   11.431%   $66.1677   $66.17   $66.15   $66.20  
  Purchase #3 $89.47   13.770%   $101.79   $101.79   $101.80   $101.80  
  Purchase #4 $74.87   12.179%   $83.9884   $83.99   $84.00   $84.00  
  Purchase #5 $167.95   11.745%   $187.6757   $187.68   $187.70   $187.70  
  Purchase #6 $8.91   5.407%   $9.3918   $9.39   $9.40   $9.40  
  Purchase #7 $6.46   13.438%   $7.3281   $7.33   $7.35   $7.30  
  7 purchase totals = $636.02       $704.9476   $704.96   $705.00   $705.00