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	$240.28	11.423%	$267.7272	$267.73	$267.75	$267.70
Purchase #2	$48.46	6.125%	$51.4282	$51.43	$51.45	$51.40
Purchase #3	$188.37	5.315%	$198.3819	$198.38	$198.40	$198.40
Purchase #4	$133.89	9.665%	$146.8305	$146.83	$146.85	$146.80
Purchase #5	$89.55	11.355%	$99.7184	$99.72	$99.70	$99.70
Purchase #6	$29.58	11.618%	$33.0166	$33.02	$33.00	$33.00
Purchase #7	$28.30	5.533%	$29.8658	$29.87	$29.85	$29.90
7 purchase totals =	$758.43		$826.9686	$826.98	$827.00	$826.90