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 $183.60   6.728%   $195.9526   $195.95   $195.95   $196.00  
  Purchase #2 $24.45   12.208%   $27.4349   $27.43   $27.45   $27.40  
  Purchase #3 $206.84   8.669%   $224.771   $224.77   $224.75   $224.80  
  Purchase #4 $222.73   6.671%   $237.5883   $237.59   $237.60   $237.60  
  Purchase #5 $209.31   7.383%   $224.7634   $224.76   $224.75   $224.80  
  Purchase #6 $218.34   12.148%   $244.8639   $244.86   $244.85   $244.90  
  Purchase #7 $182.81   7.493%   $196.508   $196.51   $196.50   $196.50  
  7 purchase totals = $1,248.08       $1,351.8821   $1,351.87   $1,351.85   $1,352.00