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 $209.86   10.770%   $232.4619   $232.46   $232.45   $232.50  
  Purchase #2 $94.32   13.377%   $106.9372   $106.94   $106.95   $106.90  
  Purchase #3 $102.95   4.587%   $107.6723   $107.67   $107.65   $107.70  
  Purchase #4 $221.63   9.391%   $242.4433   $242.44   $242.45   $242.40  
  Purchase #5 $99.70   3.183%   $102.8735   $102.87   $102.85   $102.90  
  Purchase #6 $148.81   9.552%   $163.0243   $163.02   $163.00   $163.00  
  Purchase #7 $87.41   10.833%   $96.8791   $96.88   $96.90   $96.90  
  7 purchase totals = $964.68       $1,052.2916   $1,052.28   $1,052.25   $1,052.30