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 $151.57   11.692%   $169.2916   $169.29   $169.30   $169.30  
  Purchase #2 $242.32   6.324%   $257.6443   $257.64   $257.65   $257.60  
  Purchase #3 $108.64   5.292%   $114.3892   $114.39   $114.40   $114.40  
  Purchase #4 $64.75   12.617%   $72.9195   $72.92   $72.90   $72.90  
  Purchase #5 $46.59   8.413%   $50.5096   $50.51   $50.50   $50.50  
  Purchase #6 $196.80   3.412%   $203.5148   $203.51   $203.50   $203.50  
  Purchase #7 $41.65   12.342%   $46.7904   $46.79   $46.80   $46.80  
  7 purchase totals = $852.32       $915.0594   $915.05   $915.05   $915.00