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 $84.34   11.751%   $94.2508   $94.25   $94.25   $94.30  
  Purchase #2 $192.39   9.249%   $210.1842   $210.18   $210.20   $210.20  
  Purchase #3 $247.46   5.531%   $261.147   $261.15   $261.15   $261.10  
  Purchase #4 $111.72   4.282%   $116.5039   $116.50   $116.50   $116.50  
  Purchase #5 $110.44   3.287%   $114.0702   $114.07   $114.05   $114.10  
  Purchase #6 $157.38   8.756%   $171.1602   $171.16   $171.15   $171.20  
  Purchase #7 $243.40   4.349%   $253.9855   $253.99   $254.00   $254.00  
  7 purchase totals = $1,147.13       $1,221.3018   $1,221.30   $1,221.30   $1,221.40