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	$164.74	11.211%	$183.209	$183.21	$183.20	$183.20
Purchase #2	$172.93	12.859%	$195.1671	$195.17	$195.15	$195.20
Purchase #3	$162.34	7.211%	$174.0463	$174.05	$174.05	$174.00
Purchase #4	$85.64	12.510%	$96.3536	$96.35	$96.35	$96.40
Purchase #5	$97.95	13.874%	$111.5396	$111.54	$111.55	$111.50
Purchase #6	$90.74	11.164%	$100.8702	$100.87	$100.85	$100.90
Purchase #7	$11.96	3.699%	$12.4024	$12.40	$12.40	$12.40
7 purchase totals =	$786.30		$873.5882	$873.59	$873.55	$873.60