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	$91.52	9.313%	$100.0433	$100.04	$100.05	$100.00
Purchase #2	$86.75	10.802%	$96.1207	$96.12	$96.10	$96.10
Purchase #3	$35.94	5.229%	$37.8193	$37.82	$37.80	$37.80
Purchase #4	$59.43	10.411%	$65.6173	$65.62	$65.60	$65.60
Purchase #5	$157.79	11.830%	$176.4566	$176.46	$176.45	$176.50
Purchase #6	$113.92	4.425%	$118.961	$118.96	$118.95	$119.00
Purchase #7	$17.49	3.212%	$18.0518	$18.05	$18.05	$18.10
7 purchase totals =	$562.84		$613.0700	$613.07	$613.00	$613.10