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	$85.44	5.590%	$90.2161	$90.22	$90.20	$90.20
Purchase #2	$101.57	13.123%	$114.899	$114.90	$114.90	$114.90
Purchase #3	$126.42	11.310%	$140.7181	$140.72	$140.70	$140.70
Purchase #4	$13.39	9.161%	$14.6167	$14.62	$14.60	$14.60
Purchase #5	$85.75	5.252%	$90.2536	$90.25	$90.25	$90.30
Purchase #6	$220.83	12.140%	$247.6388	$247.64	$247.65	$247.60
Purchase #7	$37.40	12.606%	$42.1146	$42.11	$42.10	$42.10
7 purchase totals =	$670.80		$740.4569	$740.46	$740.40	$740.40