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	$32.98	13.307%	$37.3686	$37.37	$37.35	$37.40
Purchase #2	$83.79	3.479%	$86.7051	$86.71	$86.70	$86.70
Purchase #3	$146.82	6.682%	$156.6305	$156.63	$156.65	$156.60
Purchase #4	$70.27	10.301%	$77.5085	$77.51	$77.50	$77.50
Purchase #5	$230.30	3.543%	$238.4595	$238.46	$238.45	$238.50
Purchase #6	$204.35	10.687%	$226.1889	$226.19	$226.20	$226.20
Purchase #7	$76.47	7.215%	$81.9873	$81.99	$82.00	$82.00
7 purchase totals =	$844.98		$904.8484	$904.86	$904.85	$904.90