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	$244.70	13.575%	$277.918	$277.92	$277.90	$277.90
Purchase #2	$99.26	3.419%	$102.6537	$102.65	$102.65	$102.70
Purchase #3	$32.95	13.651%	$37.448	$37.45	$37.45	$37.40
Purchase #4	$84.89	4.726%	$88.9019	$88.90	$88.90	$88.90
Purchase #5	$56.48	10.367%	$62.3353	$62.34	$62.35	$62.30
Purchase #6	$60.40	11.658%	$67.4414	$67.44	$67.45	$67.40
Purchase #7	$185.98	12.325%	$208.902	$208.90	$208.90	$208.90
7 purchase totals =	$764.66		$845.6003	$845.60	$845.60	$845.50