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	$230.59	11.580%	$257.2923	$257.29	$257.30	$257.30
Purchase #2	$135.50	7.575%	$145.7641	$145.76	$145.75	$145.80
Purchase #3	$103.67	7.668%	$111.6194	$111.62	$111.60	$111.60
Purchase #4	$156.37	7.605%	$168.2619	$168.26	$168.25	$168.30
Purchase #5	$67.75	13.504%	$76.899	$76.90	$76.90	$76.90
Purchase #6	$43.35	4.656%	$45.3684	$45.37	$45.35	$45.40
Purchase #7	$85.94	7.796%	$92.6399	$92.64	$92.65	$92.60
7 purchase totals =	$823.17		$897.8450	$897.84	$897.80	$897.90