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	$164.83	11.521%	$183.8201	$183.82	$183.80	$183.80
Purchase #2	$37.43	12.594%	$42.1439	$42.14	$42.15	$42.10
Purchase #3	$169.49	5.120%	$178.1679	$178.17	$178.15	$178.20
Purchase #4	$250.64	10.641%	$277.3106	$277.31	$277.30	$277.30
Purchase #5	$153.40	8.798%	$166.8961	$166.90	$166.90	$166.90
Purchase #6	$53.33	12.220%	$59.8469	$59.85	$59.85	$59.80
Purchase #7	$62.66	8.806%	$68.1778	$68.18	$68.20	$68.20
7 purchase totals =	$891.78		$976.3633	$976.37	$976.35	$976.30