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	$50.26	9.406%	$54.9875	$54.99	$55.00	$55.00
Purchase #2	$187.51	11.199%	$208.5092	$208.51	$208.50	$208.50
Purchase #3	$113.99	13.551%	$129.4368	$129.44	$129.45	$129.40
Purchase #4	$243.71	13.806%	$277.3566	$277.36	$277.35	$277.40
Purchase #5	$51.73	5.777%	$54.7184	$54.72	$54.70	$54.70
Purchase #6	$143.38	6.630%	$152.8861	$152.89	$152.90	$152.90
Purchase #7	$172.77	6.282%	$183.6234	$183.62	$183.60	$183.60
7 purchase totals =	$963.35		$1,061.5180	$1,061.53	$1,061.50	$1,061.50