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	$5.84	5.239%	$6.146	$6.15	$6.15	$6.10
Purchase #2	$50.75	12.659%	$57.1744	$57.17	$57.15	$57.20
Purchase #3	$76.81	5.325%	$80.9001	$80.90	$80.90	$80.90
Purchase #4	$85.79	11.175%	$95.377	$95.38	$95.40	$95.40
Purchase #5	$183.27	4.300%	$191.1506	$191.15	$191.15	$191.20
Purchase #6	$103.50	11.278%	$115.1727	$115.17	$115.15	$115.20
Purchase #7	$33.66	11.385%	$37.4922	$37.49	$37.50	$37.50
7 purchase totals =	$539.62		$583.4130	$583.41	$583.40	$583.50