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 $107.36   8.232%   $116.1979   $116.20   $116.20   $116.20  
  Purchase #2 $32.55   7.738%   $35.0687   $35.07   $35.05   $35.10  
  Purchase #3 $117.45   12.504%   $132.1359   $132.14   $132.15   $132.10  
  Purchase #4 $169.71   8.261%   $183.7297   $183.73   $183.75   $183.70  
  Purchase #5 $111.63   7.343%   $119.827   $119.83   $119.85   $119.80  
  Purchase #6 $238.45   4.136%   $248.3123   $248.31   $248.30   $248.30  
  Purchase #7 $154.58   8.630%   $167.9203   $167.92   $167.90   $167.90  
  7 purchase totals = $931.73       $1,003.1918   $1,003.20   $1,003.20   $1,003.10