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	$128.50	12.223%	$144.2066	$144.21	$144.20	$144.20
Purchase #2	$99.94	12.681%	$112.6134	$112.61	$112.60	$112.60
Purchase #3	$154.95	4.666%	$162.18	$162.18	$162.20	$162.20
Purchase #4	$114.61	8.543%	$124.4011	$124.40	$124.40	$124.40
Purchase #5	$57.37	5.431%	$60.4858	$60.49	$60.50	$60.50
Purchase #6	$147.96	8.530%	$160.581	$160.58	$160.60	$160.60
Purchase #7	$116.43	9.820%	$127.8634	$127.86	$127.85	$127.90
7 purchase totals =	$819.76		$892.3313	$892.33	$892.35	$892.40