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	$85.92	5.385%	$90.5468	$90.55	$90.55	$90.50
Purchase #2	$64.53	13.788%	$73.4274	$73.43	$73.45	$73.40
Purchase #3	$65.66	6.266%	$69.7743	$69.77	$69.75	$69.80
Purchase #4	$224.33	7.169%	$240.4122	$240.41	$240.40	$240.40
Purchase #5	$84.59	6.508%	$90.0951	$90.10	$90.10	$90.10
Purchase #6	$59.81	10.697%	$66.2079	$66.21	$66.20	$66.20
Purchase #7	$235.62	12.716%	$265.5814	$265.58	$265.60	$265.60
7 purchase totals =	$820.46		$896.0451	$896.05	$896.05	$896.00