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	$231.66	10.211%	$255.3148	$255.31	$255.30	$255.30
Purchase #2	$136.57	7.490%	$146.7991	$146.80	$146.80	$146.80
Purchase #3	$180.66	6.658%	$192.6883	$192.69	$192.70	$192.70
Purchase #4	$105.85	6.865%	$113.1166	$113.12	$113.10	$113.10
Purchase #5	$26.67	11.521%	$29.7427	$29.74	$29.75	$29.70
Purchase #6	$41.90	13.811%	$47.6868	$47.69	$47.70	$47.70
Purchase #7	$99.46	11.667%	$111.064	$111.06	$111.05	$111.10
7 purchase totals =	$822.77		$896.4123	$896.41	$896.40	$896.40