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	$53.55	11.698%	$59.8143	$59.81	$59.80	$59.80
Purchase #2	$60.48	7.694%	$65.1333	$65.13	$65.15	$65.10
Purchase #3	$78.87	12.699%	$88.8857	$88.89	$88.90	$88.90
Purchase #4	$64.84	12.781%	$73.1272	$73.13	$73.15	$73.10
Purchase #5	$96.58	9.524%	$105.7783	$105.78	$105.80	$105.80
Purchase #6	$13.52	10.249%	$14.9057	$14.91	$14.90	$14.90
Purchase #7	$104.26	6.175%	$110.6981	$110.70	$110.70	$110.70
7 purchase totals =	$472.10		$518.3426	$518.35	$518.40	$518.30