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 $239.46   3.119%   $246.9288   $246.93   $246.95   $246.90  
  Purchase #2 $133.29   10.247%   $146.9482   $146.95   $146.95   $146.90  
  Purchase #3 $124.38   11.137%   $138.2322   $138.23   $138.25   $138.20  
  Purchase #4 $110.32   5.855%   $116.7792   $116.78   $116.80   $116.80  
  Purchase #5 $185.38   9.600%   $203.1765   $203.18   $203.20   $203.20  
  Purchase #6 $119.82   8.456%   $129.952   $129.95   $129.95   $130.00  
  Purchase #7 $205.45   13.807%   $233.8165   $233.82   $233.80   $233.80  
  7 purchase totals = $1,118.10       $1,215.8334   $1,215.84   $1,215.90   $1,215.80