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 $239.70   11.768%   $267.9079   $267.91   $267.90   $267.90  
  Purchase #2 $168.32   4.692%   $176.2176   $176.22   $176.20   $176.20  
  Purchase #3 $232.70   3.336%   $240.4629   $240.46   $240.45   $240.50  
  Purchase #4 $81.80   9.753%   $89.778   $89.78   $89.80   $89.80  
  Purchase #5 $127.47   3.733%   $132.2285   $132.23   $132.25   $132.20  
  Purchase #6 $194.38   12.761%   $219.1848   $219.18   $219.20   $219.20  
  Purchase #7 $153.63   5.218%   $161.6464   $161.65   $161.65   $161.60  
  7 purchase totals = $1,198.00       $1,287.4261   $1,287.43   $1,287.45   $1,287.40