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	$71.73	9.596%	$78.6132	$78.61	$78.60	$78.60
Purchase #2	$216.41	3.465%	$223.9086	$223.91	$223.90	$223.90
Purchase #3	$138.32	13.614%	$157.1509	$157.15	$157.15	$157.20
Purchase #4	$117.53	11.518%	$131.0671	$131.07	$131.05	$131.10
Purchase #5	$244.62	4.690%	$256.0927	$256.09	$256.10	$256.10
Purchase #6	$193.83	6.749%	$206.9116	$206.91	$206.90	$206.90
Purchase #7	$25.61	6.694%	$27.3243	$27.32	$27.30	$27.30
7 purchase totals =	$1,008.05		$1,081.0684	$1,081.06	$1,081.00	$1,081.10