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	$44.38	6.211%	$47.1364	$47.14	$47.15	$47.10
Purchase #2	$93.53	10.246%	$103.1131	$103.11	$103.10	$103.10
Purchase #3	$217.36	13.454%	$246.6036	$246.60	$246.60	$246.60
Purchase #4	$130.89	9.345%	$143.1217	$143.12	$143.10	$143.10
Purchase #5	$60.66	10.518%	$67.0402	$67.04	$67.05	$67.00
Purchase #6	$212.49	5.306%	$223.7647	$223.76	$223.75	$223.80
Purchase #7	$59.78	3.475%	$61.8574	$61.86	$61.85	$61.90
7 purchase totals =	$819.09		$892.6371	$892.63	$892.60	$892.60