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	$48.59	13.294%	$55.0496	$55.05	$55.05	$55.00
Purchase #2	$146.98	5.468%	$155.0169	$155.02	$155.00	$155.00
Purchase #3	$43.72	4.455%	$45.6677	$45.67	$45.65	$45.70
Purchase #4	$65.71	11.512%	$73.2745	$73.27	$73.25	$73.30
Purchase #5	$16.81	6.198%	$17.8519	$17.85	$17.85	$17.90
Purchase #6	$45.59	11.333%	$50.7567	$50.76	$50.75	$50.80
Purchase #7	$85.56	10.853%	$94.8458	$94.85	$94.85	$94.80
7 purchase totals =	$452.96		$492.4631	$492.47	$492.40	$492.50