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	$22.92	9.487%	$25.0944	$25.09	$25.10	$25.10
Purchase #2	$93.46	6.215%	$99.2685	$99.27	$99.25	$99.30
Purchase #3	$161.51	13.626%	$183.5174	$183.52	$183.50	$183.50
Purchase #4	$92.76	11.647%	$103.5638	$103.56	$103.55	$103.60
Purchase #5	$138.52	3.568%	$143.4624	$143.46	$143.45	$143.50
Purchase #6	$97.97	10.382%	$108.1412	$108.14	$108.15	$108.10
Purchase #7	$202.89	6.517%	$216.1123	$216.11	$216.10	$216.10
7 purchase totals =	$810.03		$879.1600	$879.15	$879.10	$879.20