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 $62.43   6.760%   $66.6503   $66.65   $66.65   $66.70  
  Purchase #2 $191.65   8.753%   $208.4251   $208.43   $208.45   $208.40  
  Purchase #3 $62.51   8.109%   $67.5789   $67.58   $67.60   $67.60  
  Purchase #4 $178.38   7.595%   $191.928   $191.93   $191.95   $191.90  
  Purchase #5 $173.77   7.772%   $187.2754   $187.28   $187.30   $187.30  
  Purchase #6 $93.37   10.513%   $103.186   $103.19   $103.20   $103.20  
  Purchase #7 $62.31   12.237%   $69.9349   $69.93   $69.95   $69.90  
  7 purchase totals = $824.42       $894.9786   $894.99   $895.10   $895.00