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 $81.25   13.409%   $92.1448   $92.14   $92.15   $92.10  
  Purchase #2 $209.75   6.436%   $223.2495   $223.25   $223.25   $223.20  
  Purchase #3 $34.60   4.713%   $36.2307   $36.23   $36.25   $36.20  
  Purchase #4 $160.54   5.754%   $169.7775   $169.78   $169.80   $169.80  
  Purchase #5 $12.32   5.266%   $12.9688   $12.97   $12.95   $13.00  
  Purchase #6 $124.25   3.829%   $129.0075   $129.01   $129.00   $129.00  
  Purchase #7 $83.72   10.632%   $92.6211   $92.62   $92.60   $92.60  
  7 purchase totals = $706.43       $755.9999   $756.00   $756.00   $755.90