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 $245.33   12.245%   $275.3707   $275.37   $275.35   $275.40  
  Purchase #2 $86.69   9.539%   $94.9594   $94.96   $94.95   $95.00  
  Purchase #3 $159.36   6.284%   $169.3742   $169.37   $169.35   $169.40  
  Purchase #4 $114.26   3.520%   $118.282   $118.28   $118.30   $118.30  
  Purchase #5 $100.92   6.778%   $107.7604   $107.76   $107.75   $107.80  
  Purchase #6 $102.57   12.803%   $115.702   $115.70   $115.70   $115.70  
  Purchase #7 $67.62   11.335%   $75.2847   $75.28   $75.30   $75.30  
  7 purchase totals = $876.75       $956.7334   $956.72   $956.70   $956.90