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	$27.89	10.619%	$30.8516	$30.85	$30.85	$30.90
Purchase #2	$71.30	3.664%	$73.9124	$73.91	$73.90	$73.90
Purchase #3	$116.69	8.690%	$126.8304	$126.83	$126.85	$126.80
Purchase #4	$136.59	11.820%	$152.7349	$152.73	$152.75	$152.70
Purchase #5	$8.91	8.634%	$9.6793	$9.68	$9.70	$9.70
Purchase #6	$85.33	6.466%	$90.8474	$90.85	$90.85	$90.80
Purchase #7	$183.56	6.813%	$196.0659	$196.07	$196.05	$196.10
7 purchase totals =	$630.27		$680.9219	$680.92	$680.95	$680.90