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	$74.84	7.381%	$80.3639	$80.36	$80.35	$80.40
Purchase #2	$15.96	9.769%	$17.5191	$17.52	$17.50	$17.50
Purchase #3	$16.56	11.128%	$18.4028	$18.40	$18.40	$18.40
Purchase #4	$6.76	13.607%	$7.6798	$7.68	$7.70	$7.70
Purchase #5	$39.59	8.158%	$42.8198	$42.82	$42.80	$42.80
Purchase #6	$162.60	10.640%	$179.9006	$179.90	$179.90	$179.90
Purchase #7	$10.51	11.375%	$11.7055	$11.71	$11.70	$11.70
7 purchase totals =	$326.82		$358.3915	$358.39	$358.35	$358.40