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	$175.45	6.873%	$187.5087	$187.51	$187.50	$187.50
Purchase #2	$53.93	9.269%	$58.9288	$58.93	$58.95	$58.90
Purchase #3	$143.46	3.493%	$148.4711	$148.47	$148.45	$148.50
Purchase #4	$197.88	7.105%	$211.9394	$211.94	$211.95	$211.90
Purchase #5	$89.28	12.488%	$100.4293	$100.43	$100.45	$100.40
Purchase #6	$137.78	6.153%	$146.2576	$146.26	$146.25	$146.30
Purchase #7	$123.28	13.270%	$139.6393	$139.64	$139.65	$139.60
7 purchase totals =	$921.06		$993.1742	$993.18	$993.20	$993.10