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	$245.83	5.654%	$259.7292	$259.73	$259.75	$259.70
Purchase #2	$67.44	8.117%	$72.9141	$72.91	$72.90	$72.90
Purchase #3	$136.95	8.635%	$148.7756	$148.78	$148.80	$148.80
Purchase #4	$131.84	12.517%	$148.3424	$148.34	$148.35	$148.30
Purchase #5	$92.96	13.137%	$105.1722	$105.17	$105.15	$105.20
Purchase #6	$170.37	11.666%	$190.2454	$190.25	$190.25	$190.20
Purchase #7	$31.99	4.677%	$33.4862	$33.49	$33.50	$33.50
7 purchase totals =	$877.38		$958.6651	$958.67	$958.70	$958.60