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 $232.46   6.653%   $247.9256   $247.93   $247.95   $247.90  
  Purchase #2 $79.94   11.551%   $89.1739   $89.17   $89.15   $89.20  
  Purchase #3 $169.97   8.229%   $183.9568   $183.96   $183.95   $184.00  
  Purchase #4 $185.34   13.733%   $210.7927   $210.79   $210.80   $210.80  
  Purchase #5 $242.67   8.516%   $263.3358   $263.34   $263.35   $263.30  
  Purchase #6 $66.47   10.554%   $73.4852   $73.49   $73.50   $73.50  
  Purchase #7 $44.54   6.717%   $47.5318   $47.53   $47.55   $47.50  
  7 purchase totals = $1,021.39       $1,116.2018   $1,116.21   $1,116.25   $1,116.20