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	$78.99	13.502%	$89.6552	$89.66	$89.65	$89.70
Purchase #2	$27.76	5.238%	$29.2141	$29.21	$29.20	$29.20
Purchase #3	$60.39	6.721%	$64.4488	$64.45	$64.45	$64.40
Purchase #4	$66.25	7.568%	$71.2638	$71.26	$71.25	$71.30
Purchase #5	$87.71	4.270%	$91.4552	$91.46	$91.45	$91.50
Purchase #6	$9.54	10.852%	$10.5753	$10.58	$10.60	$10.60
Purchase #7	$73.50	12.531%	$82.7103	$82.71	$82.70	$82.70
7 purchase totals =	$404.14		$439.3227	$439.33	$439.30	$439.40