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	$164.33	3.396%	$169.9106	$169.91	$169.90	$169.90
Purchase #2	$63.64	12.543%	$71.6224	$71.62	$71.60	$71.60
Purchase #3	$6.74	6.214%	$7.1588	$7.16	$7.15	$7.20
Purchase #4	$33.59	5.132%	$35.3138	$35.31	$35.30	$35.30
Purchase #5	$132.29	5.197%	$139.1651	$139.17	$139.15	$139.20
Purchase #6	$153.84	11.838%	$172.0516	$172.05	$172.05	$172.10
Purchase #7	$231.73	5.549%	$244.5887	$244.59	$244.60	$244.60
7 purchase totals =	$786.16		$839.8110	$839.81	$839.75	$839.90