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	$109.39	12.826%	$123.4204	$123.42	$123.40	$123.40
Purchase #2	$206.55	10.589%	$228.4216	$228.42	$228.40	$228.40
Purchase #3	$181.63	10.312%	$200.3597	$200.36	$200.35	$200.40
Purchase #4	$137.49	11.518%	$153.3261	$153.33	$153.35	$153.30
Purchase #5	$39.54	10.685%	$43.7648	$43.76	$43.75	$43.80
Purchase #6	$53.38	6.626%	$56.917	$56.92	$56.90	$56.90
Purchase #7	$61.45	7.723%	$66.1958	$66.20	$66.20	$66.20
7 purchase totals =	$789.43		$872.4054	$872.41	$872.35	$872.40