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	$94.48	6.162%	$100.3019	$100.30	$100.30	$100.30
Purchase #2	$33.84	4.660%	$35.4169	$35.42	$35.40	$35.40
Purchase #3	$175.74	9.443%	$192.3351	$192.34	$192.35	$192.30
Purchase #4	$232.64	6.727%	$248.2897	$248.29	$248.30	$248.30
Purchase #5	$7.36	13.214%	$8.3326	$8.33	$8.35	$8.30
Purchase #6	$100.51	8.454%	$109.0071	$109.01	$109.00	$109.00
Purchase #7	$102.76	8.852%	$111.8563	$111.86	$111.85	$111.90
7 purchase totals =	$747.33		$805.5396	$805.55	$805.55	$805.50