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 $112.56   12.174%   $126.2631   $126.26   $126.25   $126.30  
  Purchase #2 $151.25   12.151%   $169.6284   $169.63   $169.65   $169.60  
  Purchase #3 $11.85   8.692%   $12.88   $12.88   $12.90   $12.90  
  Purchase #4 $98.91   9.529%   $108.3351   $108.34   $108.35   $108.30  
  Purchase #5 $243.68   4.635%   $254.9746   $254.97   $254.95   $255.00  
  Purchase #6 $125.68   3.428%   $129.9883   $129.99   $130.00   $130.00  
  Purchase #7 $197.61   3.216%   $203.9651   $203.97   $203.95   $204.00  
  7 purchase totals = $941.54       $1,006.0346   $1,006.04   $1,006.05   $1,006.10