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	$117.85	9.123%	$128.6015	$128.60	$128.60	$128.60
Purchase #2	$139.82	5.633%	$147.6961	$147.70	$147.70	$147.70
Purchase #3	$247.85	11.251%	$275.7356	$275.74	$275.75	$275.70
Purchase #4	$179.64	11.469%	$200.2429	$200.24	$200.25	$200.20
Purchase #5	$227.45	6.381%	$241.9636	$241.96	$241.95	$242.00
Purchase #6	$115.73	3.500%	$119.7806	$119.78	$119.80	$119.80
Purchase #7	$147.43	7.755%	$158.8632	$158.86	$158.85	$158.90
7 purchase totals =	$1,175.77		$1,272.8835	$1,272.88	$1,272.90	$1,272.90