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	$74.26	11.768%	$82.9989	$83.00	$83.00	$83.00
Purchase #2	$91.44	9.524%	$100.1487	$100.15	$100.15	$100.10
Purchase #3	$46.74	12.337%	$52.5063	$52.51	$52.50	$52.50
Purchase #4	$29.61	9.545%	$32.4363	$32.44	$32.45	$32.40
Purchase #5	$160.89	3.611%	$166.6997	$166.70	$166.70	$166.70
Purchase #6	$217.67	6.503%	$231.8251	$231.83	$231.85	$231.80
Purchase #7	$22.69	13.553%	$25.7652	$25.77	$25.75	$25.80
7 purchase totals =	$643.30		$692.3802	$692.40	$692.40	$692.30