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 $74.98   6.178%   $79.6123   $79.61   $79.60   $79.60  
  Purchase #2 $8.90   8.138%   $9.6243   $9.62   $9.60   $9.60  
  Purchase #3 $101.62   6.312%   $108.0343   $108.03   $108.05   $108.00  
  Purchase #4 $237.43   9.243%   $259.3757   $259.38   $259.40   $259.40  
  Purchase #5 $146.38   11.102%   $162.6311   $162.63   $162.65   $162.60  
  Purchase #6 $187.40   13.381%   $212.476   $212.48   $212.50   $212.50  
  Purchase #7 $158.28   7.185%   $169.6524   $169.65   $169.65   $169.70  
  7 purchase totals = $914.99       $1,001.4061   $1,001.40   $1,001.45   $1,001.40