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 $58.29   5.554%   $61.5274   $61.53   $61.55   $61.50  
  Purchase #2 $214.76   10.536%   $237.3871   $237.39   $237.40   $237.40  
  Purchase #3 $146.57   13.668%   $166.6032   $166.60   $166.60   $166.60  
  Purchase #4 $195.73   12.207%   $219.6228   $219.62   $219.60   $219.60  
  Purchase #5 $171.31   11.732%   $191.4081   $191.41   $191.40   $191.40  
  Purchase #6 $85.92   12.392%   $96.5672   $96.57   $96.55   $96.60  
  Purchase #7 $214.78   13.734%   $244.2779   $244.28   $244.30   $244.30  
  7 purchase totals = $1,087.36       $1,217.3937   $1,217.40   $1,217.40   $1,217.40