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	$51.99	7.200%	$55.7333	$55.73	$55.75	$55.70
Purchase #2	$64.33	3.431%	$66.5372	$66.54	$66.55	$66.50
Purchase #3	$40.63	11.568%	$45.3301	$45.33	$45.35	$45.30
Purchase #4	$99.52	13.793%	$113.2468	$113.25	$113.25	$113.20
Purchase #5	$65.68	8.158%	$71.0382	$71.04	$71.05	$71.00
Purchase #6	$31.77	10.667%	$35.1589	$35.16	$35.15	$35.20
Purchase #7	$11.73	13.837%	$13.3531	$13.35	$13.35	$13.40
7 purchase totals =	$365.65		$400.3976	$400.40	$400.45	$400.30