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	$77.31	3.846%	$80.2833	$80.28	$80.30	$80.30
Purchase #2	$160.53	9.413%	$175.6407	$175.64	$175.65	$175.60
Purchase #3	$66.43	9.793%	$72.9355	$72.94	$72.95	$72.90
Purchase #4	$32.52	8.155%	$35.172	$35.17	$35.15	$35.20
Purchase #5	$192.61	12.420%	$216.5322	$216.53	$216.55	$216.50
Purchase #6	$70.39	6.386%	$74.8851	$74.89	$74.90	$74.90
Purchase #7	$250.93	6.733%	$267.8251	$267.83	$267.85	$267.80
7 purchase totals =	$850.72		$923.2739	$923.28	$923.35	$923.20