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	$113.85	5.872%	$120.5353	$120.54	$120.55	$120.50
Purchase #2	$206.69	4.816%	$216.6442	$216.64	$216.65	$216.60
Purchase #3	$92.78	8.536%	$100.6997	$100.70	$100.70	$100.70
Purchase #4	$97.83	6.360%	$104.052	$104.05	$104.05	$104.10
Purchase #5	$229.91	7.678%	$247.5625	$247.56	$247.55	$247.60
Purchase #6	$160.25	13.390%	$181.7075	$181.71	$181.70	$181.70
Purchase #7	$59.31	3.631%	$61.4635	$61.46	$61.45	$61.50
7 purchase totals =	$960.62		$1,032.6647	$1,032.66	$1,032.65	$1,032.70