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	$93.68	7.318%	$100.5355	$100.54	$100.55	$100.50
Purchase #2	$39.89	5.490%	$42.08	$42.08	$42.10	$42.10
Purchase #3	$39.40	11.242%	$43.8293	$43.83	$43.85	$43.80
Purchase #4	$188.82	6.852%	$201.7579	$201.76	$201.75	$201.80
Purchase #5	$245.30	8.578%	$266.3418	$266.34	$266.35	$266.30
Purchase #6	$162.72	9.547%	$178.2549	$178.25	$178.25	$178.30
Purchase #7	$156.75	5.690%	$165.6691	$165.67	$165.65	$165.70
7 purchase totals =	$926.56		$998.4685	$998.47	$998.50	$998.50