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	$85.51	4.539%	$89.3913	$89.39	$89.40	$89.40
Purchase #2	$249.33	11.836%	$278.8407	$278.84	$278.85	$278.80
Purchase #3	$118.39	4.514%	$123.7341	$123.73	$123.75	$123.70
Purchase #4	$124.47	8.492%	$135.04	$135.04	$135.05	$135.00
Purchase #5	$11.55	5.575%	$12.1939	$12.19	$12.20	$12.20
Purchase #6	$131.31	13.303%	$148.7782	$148.78	$148.80	$148.80
Purchase #7	$150.92	12.177%	$169.2975	$169.30	$169.30	$169.30
7 purchase totals =	$871.48		$957.2757	$957.27	$957.35	$957.20