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	$14.35	12.793%	$16.1858	$16.19	$16.20	$16.20
Purchase #2	$135.75	8.620%	$147.4517	$147.45	$147.45	$147.50
Purchase #3	$74.98	10.613%	$82.9376	$82.94	$82.95	$82.90
Purchase #4	$247.81	12.293%	$278.2733	$278.27	$278.25	$278.30
Purchase #5	$250.48	12.838%	$282.6366	$282.64	$282.65	$282.60
Purchase #6	$55.46	6.588%	$59.1137	$59.11	$59.10	$59.10
Purchase #7	$160.76	3.707%	$166.7194	$166.72	$166.70	$166.70
7 purchase totals =	$939.59		$1,033.3181	$1,033.32	$1,033.30	$1,033.30