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	$64.41	12.685%	$72.5804	$72.58	$72.60	$72.60
Purchase #2	$200.88	6.539%	$214.0155	$214.02	$214.00	$214.00
Purchase #3	$146.76	8.451%	$159.1627	$159.16	$159.15	$159.20
Purchase #4	$147.98	13.446%	$167.8774	$167.88	$167.90	$167.90
Purchase #5	$78.60	4.782%	$82.3587	$82.36	$82.35	$82.40
Purchase #6	$20.56	5.515%	$21.6939	$21.69	$21.70	$21.70
Purchase #7	$48.92	3.864%	$50.8103	$50.81	$50.80	$50.80
7 purchase totals =	$708.11		$768.4989	$768.50	$768.50	$768.60