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	$128.29	6.474%	$136.5955	$136.60	$136.60	$136.60
Purchase #2	$91.54	6.158%	$97.177	$97.18	$97.20	$97.20
Purchase #3	$15.82	9.211%	$17.2772	$17.28	$17.30	$17.30
Purchase #4	$15.35	3.479%	$15.884	$15.88	$15.90	$15.90
Purchase #5	$130.77	12.833%	$147.5517	$147.55	$147.55	$147.60
Purchase #6	$115.69	10.133%	$127.4129	$127.41	$127.40	$127.40
Purchase #7	$99.37	7.188%	$106.5127	$106.51	$106.50	$106.50
7 purchase totals =	$596.83		$648.4110	$648.41	$648.45	$648.50