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	$160.46	7.242%	$172.0805	$172.08	$172.10	$172.10
Purchase #2	$78.61	13.352%	$89.106	$89.11	$89.10	$89.10
Purchase #3	$92.88	10.641%	$102.7634	$102.76	$102.75	$102.80
Purchase #4	$210.64	5.868%	$223.0004	$223.00	$223.00	$223.00
Purchase #5	$32.72	10.557%	$36.1743	$36.17	$36.15	$36.20
Purchase #6	$72.41	6.430%	$77.066	$77.07	$77.05	$77.10
Purchase #7	$222.29	11.250%	$247.2976	$247.30	$247.30	$247.30
7 purchase totals =	$870.01		$947.4882	$947.49	$947.45	$947.60