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 $99.30   8.189%   $107.4317   $107.43   $107.45   $107.40  
  Purchase #2 $104.64   5.862%   $110.774   $110.77   $110.75   $110.80  
  Purchase #3 $205.84   10.742%   $227.9513   $227.95   $227.95   $228.00  
  Purchase #4 $21.83   3.662%   $22.6294   $22.63   $22.65   $22.60  
  Purchase #5 $244.35   9.242%   $266.9328   $266.93   $266.95   $266.90  
  Purchase #6 $136.64   5.634%   $144.3383   $144.34   $144.35   $144.30  
  Purchase #7 $81.51   10.873%   $90.3726   $90.37   $90.35   $90.40  
  7 purchase totals = $894.11       $970.4301   $970.42   $970.45   $970.40