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	$172.38	9.248%	$188.3217	$188.32	$188.30	$188.30
Purchase #2	$99.31	12.228%	$111.4536	$111.45	$111.45	$111.50
Purchase #3	$238.69	10.695%	$264.2179	$264.22	$264.20	$264.20
Purchase #4	$8.37	11.262%	$9.3126	$9.31	$9.30	$9.30
Purchase #5	$31.99	4.851%	$33.5418	$33.54	$33.55	$33.50
Purchase #6	$64.71	13.306%	$73.3203	$73.32	$73.30	$73.30
Purchase #7	$31.37	9.346%	$34.3018	$34.30	$34.30	$34.30
7 purchase totals =	$646.82		$714.4697	$714.46	$714.40	$714.40