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	$171.62	11.210%	$190.8586	$190.86	$190.85	$190.90
Purchase #2	$238.70	13.583%	$271.1226	$271.12	$271.10	$271.10
Purchase #3	$172.44	13.610%	$195.9091	$195.91	$195.90	$195.90
Purchase #4	$19.33	9.521%	$21.1704	$21.17	$21.15	$21.20
Purchase #5	$6.73	8.170%	$7.2798	$7.28	$7.30	$7.30
Purchase #6	$75.27	3.705%	$78.0588	$78.06	$78.05	$78.10
Purchase #7	$117.35	7.802%	$126.5056	$126.51	$126.50	$126.50
7 purchase totals =	$801.44		$890.9049	$890.91	$890.85	$891.00