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	$151.78	12.865%	$171.3065	$171.31	$171.30	$171.30
Purchase #2	$152.85	10.820%	$169.3884	$169.39	$169.40	$169.40
Purchase #3	$49.95	9.109%	$54.4999	$54.50	$54.50	$54.50
Purchase #4	$75.28	8.121%	$81.3935	$81.39	$81.40	$81.40
Purchase #5	$31.38	3.261%	$32.4033	$32.40	$32.40	$32.40
Purchase #6	$101.96	9.236%	$111.377	$111.38	$111.40	$111.40
Purchase #7	$120.29	6.197%	$127.7444	$127.74	$127.75	$127.70
7 purchase totals =	$683.49		$748.1130	$748.11	$748.15	$748.10