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	$47.73	9.830%	$52.4219	$52.42	$52.40	$52.40
Purchase #2	$54.47	12.520%	$61.2896	$61.29	$61.30	$61.30
Purchase #3	$250.68	13.253%	$283.9026	$283.90	$283.90	$283.90
Purchase #4	$36.57	9.795%	$40.152	$40.15	$40.15	$40.20
Purchase #5	$77.58	9.788%	$85.1735	$85.17	$85.15	$85.20
Purchase #6	$137.26	6.573%	$146.2821	$146.28	$146.30	$146.30
Purchase #7	$197.73	9.219%	$215.9587	$215.96	$215.95	$216.00
7 purchase totals =	$802.02		$885.1804	$885.17	$885.15	$885.30