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	$146.69	12.714%	$165.3402	$165.34	$165.35	$165.30
Purchase #2	$115.76	6.483%	$123.2647	$123.26	$123.25	$123.30
Purchase #3	$106.26	10.636%	$117.5618	$117.56	$117.55	$117.60
Purchase #4	$249.84	5.161%	$262.7342	$262.73	$262.75	$262.70
Purchase #5	$143.35	12.243%	$160.9003	$160.90	$160.90	$160.90
Purchase #6	$53.61	11.343%	$59.691	$59.69	$59.70	$59.70
Purchase #7	$225.99	10.862%	$250.537	$250.54	$250.55	$250.50
7 purchase totals =	$1,041.50		$1,140.0292	$1,140.02	$1,140.05	$1,140.00