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	$138.93	3.650%	$144.0009	$144.00	$144.00	$144.00
Purchase #2	$97.58	12.452%	$109.7307	$109.73	$109.75	$109.70
Purchase #3	$97.77	7.873%	$105.4674	$105.47	$105.45	$105.50
Purchase #4	$123.47	5.428%	$130.172	$130.17	$130.15	$130.20
Purchase #5	$37.68	9.241%	$41.162	$41.16	$41.15	$41.20
Purchase #6	$35.91	4.352%	$37.4728	$37.47	$37.45	$37.50
Purchase #7	$142.77	13.362%	$161.8469	$161.85	$161.85	$161.80
7 purchase totals =	$674.11		$729.8527	$729.85	$729.80	$729.90