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 $86.60   13.557%   $98.3404   $98.34   $98.35   $98.30  
  Purchase #2 $245.48   10.694%   $271.7316   $271.73   $271.75   $271.70  
  Purchase #3 $162.70   3.162%   $167.8446   $167.84   $167.85   $167.80  
  Purchase #4 $154.74   4.341%   $161.4573   $161.46   $161.45   $161.50  
  Purchase #5 $229.25   12.116%   $257.0259   $257.03   $257.05   $257.00  
  Purchase #6 $115.62   11.690%   $129.136   $129.14   $129.15   $129.10  
  Purchase #7 $169.34   6.859%   $180.955   $180.96   $180.95   $181.00  
  7 purchase totals = $1,163.73       $1,266.4908   $1,266.50   $1,266.55   $1,266.40