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	$237.40	8.658%	$257.9541	$257.95	$257.95	$258.00
Purchase #2	$212.86	12.198%	$238.8247	$238.82	$238.80	$238.80
Purchase #3	$89.87	11.873%	$100.5403	$100.54	$100.55	$100.50
Purchase #4	$89.78	10.580%	$99.2787	$99.28	$99.30	$99.30
Purchase #5	$22.45	7.821%	$24.2058	$24.21	$24.20	$24.20
Purchase #6	$200.68	8.336%	$217.4087	$217.41	$217.40	$217.40
Purchase #7	$25.45	8.273%	$27.5555	$27.56	$27.55	$27.60
7 purchase totals =	$878.49		$965.7678	$965.77	$965.75	$965.80