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 $243.84   8.218%   $263.8788   $263.88   $263.90   $263.90  
  Purchase #2 $221.62   5.826%   $234.5316   $234.53   $234.55   $234.50  
  Purchase #3 $62.76   6.105%   $66.5915   $66.59   $66.60   $66.60  
  Purchase #4 $197.44   5.463%   $208.2261   $208.23   $208.25   $208.20  
  Purchase #5 $108.89   8.803%   $118.4756   $118.48   $118.50   $118.50  
  Purchase #6 $215.70   11.425%   $240.3437   $240.34   $240.35   $240.30  
  Purchase #7 $202.75   3.705%   $210.2619   $210.26   $210.25   $210.30  
  7 purchase totals = $1,253.00       $1,342.3092   $1,342.31   $1,342.40   $1,342.30