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	$155.65	6.852%	$166.3151	$166.32	$166.30	$166.30
Purchase #2	$145.35	12.858%	$164.0391	$164.04	$164.05	$164.00
Purchase #3	$74.37	8.198%	$80.4669	$80.47	$80.45	$80.50
Purchase #4	$242.63	11.820%	$271.3089	$271.31	$271.30	$271.30
Purchase #5	$242.68	7.770%	$261.5362	$261.54	$261.55	$261.50
Purchase #6	$86.67	5.216%	$91.1907	$91.19	$91.20	$91.20
Purchase #7	$37.37	9.225%	$40.8174	$40.82	$40.80	$40.80
7 purchase totals =	$984.72		$1,075.6743	$1,075.69	$1,075.65	$1,075.60