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	$13.79	10.466%	$15.2333	$15.23	$15.25	$15.20
Purchase #2	$19.83	10.595%	$21.931	$21.93	$21.95	$21.90
Purchase #3	$108.45	13.608%	$123.2079	$123.21	$123.20	$123.20
Purchase #4	$148.34	11.433%	$165.2997	$165.30	$165.30	$165.30
Purchase #5	$159.41	5.824%	$168.694	$168.69	$168.70	$168.70
Purchase #6	$92.64	9.355%	$101.3065	$101.31	$101.30	$101.30
Purchase #7	$194.79	9.143%	$212.5996	$212.60	$212.60	$212.60
7 purchase totals =	$737.25		$808.2720	$808.27	$808.30	$808.20