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 $58.90   3.607%   $61.0245   $61.02   $61.00   $61.00  
  Purchase #2 $89.61   12.271%   $100.606   $100.61   $100.60   $100.60  
  Purchase #3 $36.37   10.684%   $40.2558   $40.26   $40.25   $40.30  
  Purchase #4 $215.58   9.580%   $236.2326   $236.23   $236.25   $236.20  
  Purchase #5 $66.63   4.406%   $69.5657   $69.57   $69.55   $69.60  
  Purchase #6 $229.97   10.107%   $253.2131   $253.21   $253.20   $253.20  
  Purchase #7 $233.85   10.820%   $259.1526   $259.15   $259.15   $259.20  
  7 purchase totals = $930.91       $1,020.0503   $1,020.05   $1,020.00   $1,020.10