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	$44.73	13.199%	$50.6339	$50.63	$50.65	$50.60
Purchase #2	$147.89	13.504%	$167.8611	$167.86	$167.85	$167.90
Purchase #3	$162.26	6.510%	$172.8231	$172.82	$172.80	$172.80
Purchase #4	$137.39	5.636%	$145.1333	$145.13	$145.15	$145.10
Purchase #5	$84.95	3.500%	$87.9233	$87.92	$87.90	$87.90
Purchase #6	$155.51	8.601%	$168.8854	$168.89	$168.90	$168.90
Purchase #7	$29.49	3.720%	$30.587	$30.59	$30.60	$30.60
7 purchase totals =	$762.22		$823.8471	$823.84	$823.85	$823.80