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	$224.91	11.228%	$250.1629	$250.16	$250.15	$250.20
Purchase #2	$32.72	13.226%	$37.0475	$37.05	$37.05	$37.00
Purchase #3	$108.66	9.329%	$118.7969	$118.80	$118.80	$118.80
Purchase #4	$28.87	13.727%	$32.833	$32.83	$32.85	$32.80
Purchase #5	$33.32	9.626%	$36.5274	$36.53	$36.55	$36.50
Purchase #6	$40.99	5.665%	$43.3121	$43.31	$43.30	$43.30
Purchase #7	$42.54	6.622%	$45.357	$45.36	$45.35	$45.40
7 purchase totals =	$512.01		$564.0368	$564.04	$564.05	$564.00