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	$147.58	12.543%	$166.091	$166.09	$166.10	$166.10
Purchase #2	$149.62	6.596%	$159.4889	$159.49	$159.50	$159.50
Purchase #3	$33.53	11.662%	$37.4403	$37.44	$37.45	$37.40
Purchase #4	$135.47	7.170%	$145.1832	$145.18	$145.20	$145.20
Purchase #5	$173.74	13.155%	$196.5955	$196.60	$196.60	$196.60
Purchase #6	$32.64	10.142%	$35.9503	$35.95	$35.95	$36.00
Purchase #7	$80.71	11.661%	$90.1216	$90.12	$90.10	$90.10
7 purchase totals =	$753.29		$830.8708	$830.87	$830.90	$830.90