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	$117.96	5.492%	$124.4384	$124.44	$124.45	$124.40
Purchase #2	$158.95	4.222%	$165.6609	$165.66	$165.65	$165.70
Purchase #3	$58.61	10.709%	$64.8865	$64.89	$64.90	$64.90
Purchase #4	$192.43	11.568%	$214.6903	$214.69	$214.70	$214.70
Purchase #5	$83.78	5.631%	$88.4977	$88.50	$88.50	$88.50
Purchase #6	$37.46	12.250%	$42.0489	$42.05	$42.05	$42.00
Purchase #7	$143.98	8.224%	$155.8209	$155.82	$155.80	$155.80
7 purchase totals =	$793.17		$856.0436	$856.05	$856.05	$856.00