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 $228.82   11.701%   $255.5942   $255.59   $255.60   $255.60  
  Purchase #2 $145.74   5.391%   $153.5968   $153.60   $153.60   $153.60  
  Purchase #3 $124.47   3.501%   $128.8277   $128.83   $128.85   $128.80  
  Purchase #4 $242.37   10.550%   $267.94   $267.94   $267.95   $267.90  
  Purchase #5 $238.59   8.290%   $258.3691   $258.37   $258.35   $258.40  
  Purchase #6 $100.34   13.612%   $113.9983   $114.00   $114.00   $114.00  
  Purchase #7 $87.99   10.583%   $97.302   $97.30   $97.30   $97.30  
  7 purchase totals = $1,168.32       $1,275.6281   $1,275.63   $1,275.65   $1,275.60