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	$239.91	12.350%	$269.5389	$269.54	$269.55	$269.50
Purchase #2	$147.35	5.813%	$155.9155	$155.92	$155.90	$155.90
Purchase #3	$214.81	13.609%	$244.0435	$244.04	$244.05	$244.00
Purchase #4	$150.50	5.236%	$158.3802	$158.38	$158.40	$158.40
Purchase #5	$89.56	12.428%	$100.6905	$100.69	$100.70	$100.70
Purchase #6	$76.55	8.557%	$83.1004	$83.10	$83.10	$83.10
Purchase #7	$188.42	8.431%	$204.3057	$204.31	$204.30	$204.30
7 purchase totals =	$1,107.10		$1,215.9747	$1,215.98	$1,216.00	$1,215.90