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	$105.73	12.762%	$119.2233	$119.22	$119.20	$119.20
Purchase #2	$39.26	6.128%	$41.6659	$41.67	$41.65	$41.70
Purchase #3	$116.54	7.580%	$125.3737	$125.37	$125.35	$125.40
Purchase #4	$53.70	10.846%	$59.5243	$59.52	$59.50	$59.50
Purchase #5	$189.59	3.626%	$196.4645	$196.46	$196.45	$196.50
Purchase #6	$13.42	8.201%	$14.5206	$14.52	$14.50	$14.50
Purchase #7	$66.94	11.531%	$74.6589	$74.66	$74.65	$74.70
7 purchase totals =	$585.18		$631.4312	$631.42	$631.30	$631.50