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	$145.29	3.119%	$149.8216	$149.82	$149.80	$149.80
Purchase #2	$190.85	13.704%	$217.0041	$217.00	$217.00	$217.00
Purchase #3	$92.47	12.307%	$103.8503	$103.85	$103.85	$103.90
Purchase #4	$23.43	3.760%	$24.311	$24.31	$24.30	$24.30
Purchase #5	$132.90	13.147%	$150.3724	$150.37	$150.35	$150.40
Purchase #6	$88.32	12.631%	$99.4757	$99.48	$99.50	$99.50
Purchase #7	$68.44	4.222%	$71.3295	$71.33	$71.35	$71.30
7 purchase totals =	$741.70		$816.1646	$816.16	$816.15	$816.20