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	$10.72	13.611%	$12.1791	$12.18	$12.20	$12.20
Purchase #2	$88.92	12.763%	$100.2689	$100.27	$100.25	$100.30
Purchase #3	$39.36	3.642%	$40.7935	$40.79	$40.80	$40.80
Purchase #4	$127.68	11.274%	$142.0746	$142.07	$142.05	$142.10
Purchase #5	$73.41	8.171%	$79.4083	$79.41	$79.40	$79.40
Purchase #6	$93.27	9.748%	$102.362	$102.36	$102.35	$102.40
Purchase #7	$86.74	6.343%	$92.2419	$92.24	$92.25	$92.20
7 purchase totals =	$520.10		$569.3283	$569.32	$569.30	$569.40