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	$199.80	11.378%	$222.5332	$222.53	$222.55	$222.50
Purchase #2	$229.60	6.650%	$244.8684	$244.87	$244.85	$244.90
Purchase #3	$134.78	5.694%	$142.4544	$142.45	$142.45	$142.50
Purchase #4	$30.56	7.612%	$32.8862	$32.89	$32.90	$32.90
Purchase #5	$171.41	6.228%	$182.0854	$182.09	$182.10	$182.10
Purchase #6	$247.39	3.853%	$256.9219	$256.92	$256.90	$256.90
Purchase #7	$176.47	6.761%	$188.4011	$188.40	$188.40	$188.40
7 purchase totals =	$1,190.01		$1,270.1506	$1,270.15	$1,270.15	$1,270.20