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	$156.78	12.377%	$176.1847	$176.18	$176.20	$176.20
Purchase #2	$70.72	11.110%	$78.577	$78.58	$78.60	$78.60
Purchase #3	$17.82	6.114%	$18.9095	$18.91	$18.90	$18.90
Purchase #4	$90.76	9.292%	$99.1934	$99.19	$99.20	$99.20
Purchase #5	$6.40	9.130%	$6.9843	$6.98	$7.00	$7.00
Purchase #6	$9.62	7.201%	$10.3127	$10.31	$10.30	$10.30
Purchase #7	$148.56	9.337%	$162.431	$162.43	$162.45	$162.40
7 purchase totals =	$500.66		$552.5926	$552.58	$552.65	$552.60