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	$69.82	3.202%	$72.0556	$72.06	$72.05	$72.10
Purchase #2	$146.26	10.292%	$161.3131	$161.31	$161.30	$161.30
Purchase #3	$33.38	7.394%	$35.8481	$35.85	$35.85	$35.80
Purchase #4	$139.73	11.470%	$155.757	$155.76	$155.75	$155.80
Purchase #5	$224.49	12.359%	$252.2347	$252.23	$252.25	$252.20
Purchase #6	$29.89	8.420%	$32.4067	$32.41	$32.40	$32.40
Purchase #7	$91.96	9.198%	$100.4185	$100.42	$100.40	$100.40
7 purchase totals =	$735.53		$810.0337	$810.04	$810.00	$810.00