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	$103.37	7.555%	$111.1796	$111.18	$111.20	$111.20
Purchase #2	$26.55	3.644%	$27.5175	$27.52	$27.50	$27.50
Purchase #3	$136.31	7.666%	$146.7595	$146.76	$146.75	$146.80
Purchase #4	$124.42	4.313%	$129.7862	$129.79	$129.80	$129.80
Purchase #5	$176.51	9.226%	$192.7948	$192.79	$192.80	$192.80
Purchase #6	$72.72	8.471%	$78.8801	$78.88	$78.90	$78.90
Purchase #7	$20.55	13.141%	$23.2505	$23.25	$23.25	$23.30
7 purchase totals =	$660.43		$710.1682	$710.17	$710.20	$710.30