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	$7.65	3.400%	$7.9101	$7.91	$7.90	$7.90
Purchase #2	$40.37	11.430%	$44.9843	$44.98	$45.00	$45.00
Purchase #3	$57.78	10.663%	$63.9411	$63.94	$63.95	$63.90
Purchase #4	$10.33	5.794%	$10.9285	$10.93	$10.95	$10.90
Purchase #5	$114.94	8.409%	$124.6053	$124.61	$124.60	$124.60
Purchase #6	$143.58	8.595%	$155.9207	$155.92	$155.90	$155.90
Purchase #7	$72.89	7.198%	$78.1366	$78.14	$78.15	$78.10
7 purchase totals =	$447.54		$486.4266	$486.43	$486.45	$486.30