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	$70.53	10.817%	$78.1592	$78.16	$78.15	$78.20
Purchase #2	$195.42	13.122%	$221.063	$221.06	$221.05	$221.10
Purchase #3	$100.99	10.781%	$111.8777	$111.88	$111.90	$111.90
Purchase #4	$234.91	5.526%	$247.8911	$247.89	$247.90	$247.90
Purchase #5	$193.95	8.150%	$209.7569	$209.76	$209.75	$209.80
Purchase #6	$17.75	11.405%	$19.7744	$19.77	$19.75	$19.80
Purchase #7	$56.77	9.521%	$62.1751	$62.18	$62.20	$62.20
7 purchase totals =	$870.32		$950.6974	$950.70	$950.70	$950.90