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 $141.48   12.745%   $159.5116   $159.51   $159.50   $159.50  
  Purchase #2 $244.54   7.267%   $262.3107   $262.31   $262.30   $262.30  
  Purchase #3 $159.49   6.762%   $170.2747   $170.27   $170.25   $170.30  
  Purchase #4 $125.33   3.144%   $129.2704   $129.27   $129.25   $129.30  
  Purchase #5 $153.84   3.764%   $159.6305   $159.63   $159.65   $159.60  
  Purchase #6 $170.41   9.551%   $186.6859   $186.69   $186.70   $186.70  
  Purchase #7 $60.67   8.351%   $65.7366   $65.74   $65.75   $65.70  
  7 purchase totals = $1,055.76       $1,133.4204   $1,133.42   $1,133.40   $1,133.40