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	$97.57	7.111%	$104.5082	$104.51	$104.50	$104.50
Purchase #2	$55.34	5.591%	$58.4341	$58.43	$58.45	$58.40
Purchase #3	$116.57	10.582%	$128.9054	$128.91	$128.90	$128.90
Purchase #4	$180.92	10.301%	$199.5566	$199.56	$199.55	$199.60
Purchase #5	$122.65	12.114%	$137.5078	$137.51	$137.50	$137.50
Purchase #6	$167.32	4.162%	$174.2839	$174.28	$174.30	$174.30
Purchase #7	$19.81	12.846%	$22.3548	$22.35	$22.35	$22.40
7 purchase totals =	$760.18		$825.5508	$825.55	$825.55	$825.60