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	$53.72	12.592%	$60.4844	$60.48	$60.50	$60.50
Purchase #2	$73.97	12.397%	$83.1401	$83.14	$83.15	$83.10
Purchase #3	$134.77	12.781%	$151.995	$152.00	$152.00	$152.00
Purchase #4	$101.62	10.476%	$112.2657	$112.27	$112.25	$112.30
Purchase #5	$65.61	5.708%	$69.355	$69.36	$69.35	$69.40
Purchase #6	$54.89	8.427%	$59.5156	$59.52	$59.50	$59.50
Purchase #7	$113.45	3.388%	$117.2937	$117.29	$117.30	$117.30
7 purchase totals =	$598.03		$654.0495	$654.06	$654.05	$654.10