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	$44.76	13.199%	$50.6679	$50.67	$50.65	$50.70
Purchase #2	$105.25	11.109%	$116.9422	$116.94	$116.95	$116.90
Purchase #3	$55.40	8.420%	$60.0647	$60.06	$60.05	$60.10
Purchase #4	$58.79	5.749%	$62.1698	$62.17	$62.15	$62.20
Purchase #5	$172.36	7.656%	$185.5559	$185.56	$185.55	$185.60
Purchase #6	$144.54	13.699%	$164.3405	$164.34	$164.35	$164.30
Purchase #7	$132.56	9.506%	$145.1612	$145.16	$145.15	$145.20
7 purchase totals =	$713.66		$784.9022	$784.90	$784.85	$785.00