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	$26.82	10.228%	$29.5631	$29.56	$29.55	$29.60
Purchase #2	$46.56	4.630%	$48.7157	$48.72	$48.70	$48.70
Purchase #3	$84.70	7.533%	$91.0805	$91.08	$91.10	$91.10
Purchase #4	$105.82	3.227%	$109.2348	$109.23	$109.25	$109.20
Purchase #5	$123.32	6.412%	$131.2273	$131.23	$131.25	$131.20
Purchase #6	$194.62	8.236%	$210.6489	$210.65	$210.65	$210.60
Purchase #7	$35.78	11.200%	$39.7874	$39.79	$39.80	$39.80
7 purchase totals =	$617.62		$660.2577	$660.26	$660.30	$660.20