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 $83.91   11.673%   $93.7048   $93.70   $93.70   $93.70  
  Purchase #2 $112.62   4.760%   $117.9807   $117.98   $118.00   $118.00  
  Purchase #3 $235.55   6.238%   $250.2436   $250.24   $250.25   $250.20  
  Purchase #4 $104.96   11.251%   $116.769   $116.77   $116.75   $116.80  
  Purchase #5 $62.54   6.719%   $66.7421   $66.74   $66.75   $66.70  
  Purchase #6 $250.27   9.614%   $274.331   $274.33   $274.35   $274.30  
  Purchase #7 $26.82   5.664%   $28.3391   $28.34   $28.35   $28.30  
  7 purchase totals = $876.67       $948.1103   $948.10   $948.15   $948.00