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 $181.64   13.792%   $206.6918   $206.69   $206.70   $206.70  
  Purchase #2 $151.41   6.141%   $160.7081   $160.71   $160.70   $160.70  
  Purchase #3 $197.67   3.489%   $204.5667   $204.57   $204.55   $204.60  
  Purchase #4 $215.34   6.216%   $228.7255   $228.73   $228.75   $228.70  
  Purchase #5 $214.66   8.219%   $232.3029   $232.30   $232.30   $232.30  
  Purchase #6 $176.66   5.263%   $185.9576   $185.96   $185.95   $186.00  
  Purchase #7 $139.42   9.298%   $152.3833   $152.38   $152.40   $152.40  
  7 purchase totals = $1,276.80       $1,371.3359   $1,371.34   $1,371.35   $1,371.40