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	$113.72	11.541%	$126.8444	$126.84	$126.85	$126.80
Purchase #2	$81.94	6.104%	$86.9416	$86.94	$86.95	$86.90
Purchase #3	$23.50	13.279%	$26.6206	$26.62	$26.60	$26.60
Purchase #4	$46.51	8.686%	$50.5499	$50.55	$50.55	$50.50
Purchase #5	$130.55	11.527%	$145.5985	$145.60	$145.60	$145.60
Purchase #6	$89.29	5.279%	$94.0036	$94.00	$94.00	$94.00
Purchase #7	$100.33	11.245%	$111.6121	$111.61	$111.60	$111.60
7 purchase totals =	$585.84		$642.1707	$642.16	$642.15	$642.00