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	$139.41	3.632%	$144.4734	$144.47	$144.45	$144.50
Purchase #2	$121.27	7.502%	$130.3677	$130.37	$130.35	$130.40
Purchase #3	$88.66	13.727%	$100.8304	$100.83	$100.85	$100.80
Purchase #4	$76.83	13.595%	$87.275	$87.28	$87.30	$87.30
Purchase #5	$168.95	6.450%	$179.8473	$179.85	$179.85	$179.80
Purchase #6	$185.81	10.400%	$205.1342	$205.13	$205.15	$205.10
Purchase #7	$143.66	8.381%	$155.7001	$155.70	$155.70	$155.70
7 purchase totals =	$924.59		$1,003.6281	$1,003.63	$1,003.65	$1,003.60