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	$218.78	8.468%	$237.3063	$237.31	$237.30	$237.30
Purchase #2	$134.48	11.669%	$150.1725	$150.17	$150.15	$150.20
Purchase #3	$134.60	4.469%	$140.6153	$140.62	$140.60	$140.60
Purchase #4	$45.46	3.136%	$46.8856	$46.89	$46.90	$46.90
Purchase #5	$19.43	7.704%	$20.9269	$20.93	$20.95	$20.90
Purchase #6	$197.67	5.861%	$209.2554	$209.26	$209.25	$209.30
Purchase #7	$192.88	3.730%	$200.0744	$200.07	$200.05	$200.10
7 purchase totals =	$943.30		$1,005.2364	$1,005.25	$1,005.20	$1,005.30