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 $236.34   11.478%   $263.4671   $263.47   $263.45   $263.50  
  Purchase #2 $87.88   10.482%   $97.0916   $97.09   $97.10   $97.10  
  Purchase #3 $105.72   10.576%   $116.9009   $116.90   $116.90   $116.90  
  Purchase #4 $44.96   9.557%   $49.2568   $49.26   $49.25   $49.30  
  Purchase #5 $245.70   6.407%   $261.442   $261.44   $261.45   $261.40  
  Purchase #6 $221.29   11.104%   $245.862   $245.86   $245.85   $245.90  
  Purchase #7 $29.90   10.200%   $32.9498   $32.95   $32.95   $32.90  
  7 purchase totals = $971.79       $1,066.9702   $1,066.97   $1,066.95   $1,067.00