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 $61.33   8.311%   $66.4271   $66.43   $66.45   $66.40  
  Purchase #2 $209.37   4.567%   $218.9319   $218.93   $218.95   $218.90  
  Purchase #3 $53.96   12.268%   $60.5798   $60.58   $60.60   $60.60  
  Purchase #4 $44.85   13.334%   $50.8303   $50.83   $50.85   $50.80  
  Purchase #5 $237.68   9.576%   $260.4402   $260.44   $260.45   $260.40  
  Purchase #6 $15.44   3.159%   $15.9277   $15.93   $15.95   $15.90  
  Purchase #7 $223.34   5.740%   $236.1597   $236.16   $236.15   $236.20  
  7 purchase totals = $845.97       $909.2967   $909.30   $909.40   $909.20