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	$146.94	7.220%	$157.5491	$157.55	$157.55	$157.50
Purchase #2	$34.85	10.137%	$38.3827	$38.38	$38.40	$38.40
Purchase #3	$235.48	10.720%	$260.7235	$260.72	$260.70	$260.70
Purchase #4	$8.57	5.707%	$9.0591	$9.06	$9.05	$9.10
Purchase #5	$28.66	12.186%	$32.1525	$32.15	$32.15	$32.20
Purchase #6	$78.61	10.744%	$87.0559	$87.06	$87.05	$87.10
Purchase #7	$78.61	5.348%	$82.8141	$82.81	$82.80	$82.80
7 purchase totals =	$611.72		$667.7369	$667.73	$667.70	$667.80