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	$181.47	3.333%	$187.5184	$187.52	$187.50	$187.50
Purchase #2	$38.75	7.313%	$41.5838	$41.58	$41.60	$41.60
Purchase #3	$86.47	5.760%	$91.4507	$91.45	$91.45	$91.50
Purchase #4	$116.53	12.610%	$131.2244	$131.22	$131.20	$131.20
Purchase #5	$125.68	11.786%	$140.4926	$140.49	$140.50	$140.50
Purchase #6	$30.66	9.305%	$33.5129	$33.51	$33.50	$33.50
Purchase #7	$40.83	13.170%	$46.2073	$46.21	$46.20	$46.20
7 purchase totals =	$620.39		$671.9901	$671.98	$671.95	$672.00