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 $246.61   10.361%   $272.1613   $272.16   $272.15   $272.20  
  Purchase #2 $20.45   5.505%   $21.5758   $21.58   $21.60   $21.60  
  Purchase #3 $201.93   8.383%   $218.8578   $218.86   $218.85   $218.90  
  Purchase #4 $237.26   7.836%   $255.8517   $255.85   $255.85   $255.90  
  Purchase #5 $69.32   8.205%   $75.0077   $75.01   $75.00   $75.00  
  Purchase #6 $153.42   3.543%   $158.8557   $158.86   $158.85   $158.90  
  Purchase #7 $237.97   9.314%   $260.1345   $260.13   $260.15   $260.10  
  7 purchase totals = $1,166.96       $1,262.4445   $1,262.45   $1,262.45   $1,262.60