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	$221.25	12.234%	$248.3177	$248.32	$248.30	$248.30
Purchase #2	$144.52	10.738%	$160.0386	$160.04	$160.05	$160.00
Purchase #3	$61.79	11.341%	$68.7976	$68.80	$68.80	$68.80
Purchase #4	$142.51	12.637%	$160.519	$160.52	$160.50	$160.50
Purchase #5	$17.85	5.132%	$18.7661	$18.77	$18.75	$18.80
Purchase #6	$98.72	13.372%	$111.9208	$111.92	$111.90	$111.90
Purchase #7	$196.66	12.623%	$221.4844	$221.48	$221.50	$221.50
7 purchase totals =	$883.30		$989.8442	$989.85	$989.80	$989.80