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	$136.81	9.609%	$149.9561	$149.96	$149.95	$150.00
Purchase #2	$89.41	13.300%	$101.3015	$101.30	$101.30	$101.30
Purchase #3	$142.70	6.283%	$151.6658	$151.67	$151.65	$151.70
Purchase #4	$42.46	10.539%	$46.9349	$46.93	$46.95	$46.90
Purchase #5	$47.34	3.274%	$48.8899	$48.89	$48.90	$48.90
Purchase #6	$67.30	5.718%	$71.1482	$71.15	$71.15	$71.10
Purchase #7	$27.60	3.705%	$28.6226	$28.62	$28.60	$28.60
7 purchase totals =	$553.62		$598.5190	$598.52	$598.50	$598.50