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	$128.53	8.669%	$139.6723	$139.67	$139.65	$139.70
Purchase #2	$210.97	9.123%	$230.2168	$230.22	$230.20	$230.20
Purchase #3	$164.47	12.559%	$185.1258	$185.13	$185.15	$185.10
Purchase #4	$97.31	3.342%	$100.5621	$100.56	$100.55	$100.60
Purchase #5	$25.76	13.821%	$29.3203	$29.32	$29.30	$29.30
Purchase #6	$54.32	3.340%	$56.1343	$56.13	$56.15	$56.10
Purchase #7	$207.48	11.586%	$231.5186	$231.52	$231.50	$231.50
7 purchase totals =	$888.84		$972.5502	$972.55	$972.50	$972.50