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	$81.68	10.730%	$90.4443	$90.44	$90.45	$90.40
Purchase #2	$152.85	7.184%	$163.8307	$163.83	$163.85	$163.80
Purchase #3	$49.28	11.431%	$54.9132	$54.91	$54.90	$54.90
Purchase #4	$223.70	8.703%	$243.1686	$243.17	$243.15	$243.20
Purchase #5	$14.77	7.152%	$15.8264	$15.83	$15.85	$15.80
Purchase #6	$80.82	10.220%	$89.0798	$89.08	$89.10	$89.10
Purchase #7	$67.87	4.243%	$70.7497	$70.75	$70.75	$70.70
7 purchase totals =	$670.97		$728.0127	$728.01	$728.05	$727.90