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	$50.41	8.539%	$54.7145	$54.71	$54.70	$54.70
Purchase #2	$27.76	5.250%	$29.2174	$29.22	$29.20	$29.20
Purchase #3	$26.76	6.411%	$28.4756	$28.48	$28.50	$28.50
Purchase #4	$228.51	11.650%	$255.1314	$255.13	$255.15	$255.10
Purchase #5	$128.26	9.743%	$140.7564	$140.76	$140.75	$140.80
Purchase #6	$62.61	6.729%	$66.823	$66.82	$66.80	$66.80
Purchase #7	$82.79	4.488%	$86.5056	$86.51	$86.50	$86.50
7 purchase totals =	$607.10		$661.6239	$661.63	$661.60	$661.60