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 $207.34   3.339%   $214.2631   $214.26   $214.25   $214.30  
  Purchase #2 $249.65   8.295%   $270.3585   $270.36   $270.35   $270.40  
  Purchase #3 $10.75   11.223%   $11.9565   $11.96   $11.95   $12.00  
  Purchase #4 $21.29   5.166%   $22.3898   $22.39   $22.40   $22.40  
  Purchase #5 $133.87   11.367%   $149.087   $149.09   $149.10   $149.10  
  Purchase #6 $63.57   9.329%   $69.5004   $69.50   $69.50   $69.50  
  Purchase #7 $177.30   11.198%   $197.1541   $197.15   $197.15   $197.20  
  7 purchase totals = $863.77       $934.7094   $934.71   $934.70   $934.90