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	$93.51	6.441%	$99.533	$99.53	$99.55	$99.50
Purchase #2	$193.84	10.823%	$214.8193	$214.82	$214.80	$214.80
Purchase #3	$155.42	11.507%	$173.3042	$173.30	$173.30	$173.30
Purchase #4	$126.73	7.746%	$136.5465	$136.55	$136.55	$136.50
Purchase #5	$45.40	6.644%	$48.4164	$48.42	$48.40	$48.40
Purchase #6	$52.57	12.813%	$59.3058	$59.31	$59.30	$59.30
Purchase #7	$150.60	7.652%	$162.1239	$162.12	$162.10	$162.10
7 purchase totals =	$818.07		$894.0491	$894.05	$894.00	$893.90