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	$168.91	9.846%	$185.5409	$185.54	$185.55	$185.50
Purchase #2	$140.64	12.761%	$158.5871	$158.59	$158.60	$158.60
Purchase #3	$117.45	6.712%	$125.3332	$125.33	$125.35	$125.30
Purchase #4	$229.78	13.440%	$260.6624	$260.66	$260.65	$260.70
Purchase #5	$40.94	10.647%	$45.2989	$45.30	$45.30	$45.30
Purchase #6	$168.38	6.436%	$179.2169	$179.22	$179.20	$179.20
Purchase #7	$204.86	13.820%	$233.1717	$233.17	$233.15	$233.20
7 purchase totals =	$1,070.96		$1,187.8111	$1,187.81	$1,187.80	$1,187.80