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 $244.93   5.823%   $259.1923   $259.19   $259.20   $259.20  
  Purchase #2 $182.30   3.187%   $188.1099   $188.11   $188.10   $188.10  
  Purchase #3 $21.36   8.384%   $23.1508   $23.15   $23.15   $23.20  
  Purchase #4 $74.83   12.156%   $83.9263   $83.93   $83.95   $83.90  
  Purchase #5 $110.92   7.492%   $119.2301   $119.23   $119.25   $119.20  
  Purchase #6 $239.74   10.168%   $264.1168   $264.12   $264.10   $264.10  
  Purchase #7 $249.86   10.783%   $276.8024   $276.80   $276.80   $276.80  
  7 purchase totals = $1,123.94       $1,214.5286   $1,214.53   $1,214.55   $1,214.50