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	$248.95	11.642%	$277.9328	$277.93	$277.95	$277.90
Purchase #2	$53.27	9.107%	$58.1213	$58.12	$58.10	$58.10
Purchase #3	$33.95	11.716%	$37.9276	$37.93	$37.95	$37.90
Purchase #4	$43.40	5.103%	$45.6147	$45.61	$45.60	$45.60
Purchase #5	$21.94	12.552%	$24.6939	$24.69	$24.70	$24.70
Purchase #6	$204.91	9.174%	$223.7084	$223.71	$223.70	$223.70
Purchase #7	$41.78	4.362%	$43.6024	$43.60	$43.60	$43.60
7 purchase totals =	$648.20		$711.6011	$711.59	$711.60	$711.50