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	$153.59	12.367%	$172.5845	$172.58	$172.60	$172.60
Purchase #2	$240.95	13.769%	$274.1264	$274.13	$274.15	$274.10
Purchase #3	$79.53	7.763%	$85.7039	$85.70	$85.70	$85.70
Purchase #4	$37.27	9.749%	$40.9035	$40.90	$40.90	$40.90
Purchase #5	$236.33	4.458%	$246.8656	$246.87	$246.85	$246.90
Purchase #6	$247.58	11.233%	$275.3907	$275.39	$275.40	$275.40
Purchase #7	$138.92	4.871%	$145.6868	$145.69	$145.70	$145.70
7 purchase totals =	$1,134.17		$1,241.2614	$1,241.26	$1,241.30	$1,241.30