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	$138.26	12.588%	$155.6642	$155.66	$155.65	$155.70
Purchase #2	$217.98	5.162%	$229.2321	$229.23	$229.25	$229.20
Purchase #3	$105.39	5.440%	$111.1232	$111.12	$111.10	$111.10
Purchase #4	$198.78	12.562%	$223.7507	$223.75	$223.75	$223.80
Purchase #5	$202.81	12.103%	$227.3561	$227.36	$227.35	$227.40
Purchase #6	$248.31	13.417%	$281.6258	$281.63	$281.65	$281.60
Purchase #7	$144.82	7.812%	$156.1333	$156.13	$156.15	$156.10
7 purchase totals =	$1,256.35		$1,384.8854	$1,384.88	$1,384.90	$1,384.90