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	$135.66	7.798%	$146.2388	$146.24	$146.25	$146.20
Purchase #2	$37.33	9.152%	$40.7464	$40.75	$40.75	$40.70
Purchase #3	$151.83	5.283%	$159.8512	$159.85	$159.85	$159.90
Purchase #4	$78.51	5.288%	$82.6616	$82.66	$82.65	$82.70
Purchase #5	$202.72	8.212%	$219.3674	$219.37	$219.35	$219.40
Purchase #6	$221.94	5.831%	$234.8813	$234.88	$234.90	$234.90
Purchase #7	$230.68	13.184%	$261.0929	$261.09	$261.10	$261.10
7 purchase totals =	$1,058.67		$1,144.8396	$1,144.84	$1,144.85	$1,144.90