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	$74.28	6.236%	$78.9121	$78.91	$78.90	$78.90
Purchase #2	$38.90	4.749%	$40.7474	$40.75	$40.75	$40.70
Purchase #3	$206.45	4.515%	$215.7712	$215.77	$215.75	$215.80
Purchase #4	$79.39	10.278%	$87.5497	$87.55	$87.55	$87.50
Purchase #5	$152.78	6.687%	$162.9964	$163.00	$163.00	$163.00
Purchase #6	$139.52	11.407%	$155.435	$155.44	$155.45	$155.40
Purchase #7	$30.46	7.607%	$32.7771	$32.78	$32.80	$32.80
7 purchase totals =	$721.78		$774.1889	$774.20	$774.20	$774.10