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 $63.39   6.239%   $67.3449   $67.34   $67.35   $67.30  
  Purchase #2 $157.45   7.728%   $169.6177   $169.62   $169.60   $169.60  
  Purchase #3 $77.79   13.322%   $88.1532   $88.15   $88.15   $88.20  
  Purchase #4 $216.28   13.355%   $245.1642   $245.16   $245.15   $245.20  
  Purchase #5 $36.29   10.209%   $39.9948   $39.99   $40.00   $40.00  
  Purchase #6 $127.89   13.692%   $145.4007   $145.40   $145.40   $145.40  
  Purchase #7 $186.74   10.105%   $205.6101   $205.61   $205.60   $205.60  
  7 purchase totals = $865.83       $961.2856   $961.27   $961.25   $961.30