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 $242.91   5.697%   $256.7486   $256.75   $256.75   $256.70  
  Purchase #2 $133.58   8.385%   $144.7807   $144.78   $144.80   $144.80  
  Purchase #3 $62.98   12.365%   $70.7675   $70.77   $70.75   $70.80  
  Purchase #4 $214.95   4.677%   $225.0032   $225.00   $225.00   $225.00  
  Purchase #5 $101.43   7.742%   $109.2827   $109.28   $109.30   $109.30  
  Purchase #6 $153.93   4.770%   $161.2725   $161.27   $161.25   $161.30  
  Purchase #7 $219.81   5.677%   $232.2886   $232.29   $232.30   $232.30  
  7 purchase totals = $1,129.59       $1,200.1438   $1,200.14   $1,200.15   $1,200.20