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	$33.88	4.707%	$35.4747	$35.47	$35.45	$35.50
Purchase #2	$18.54	13.514%	$21.0455	$21.05	$21.05	$21.00
Purchase #3	$59.63	13.407%	$67.6246	$67.62	$67.60	$67.60
Purchase #4	$139.63	5.278%	$146.9997	$147.00	$147.00	$147.00
Purchase #5	$108.57	5.142%	$114.1527	$114.15	$114.15	$114.20
Purchase #6	$219.98	9.555%	$240.9991	$241.00	$241.00	$241.00
Purchase #7	$37.37	10.791%	$41.4026	$41.40	$41.40	$41.40
7 purchase totals =	$617.60		$667.6989	$667.69	$667.65	$667.70