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	$95.64	4.456%	$99.9017	$99.90	$99.90	$99.90
Purchase #2	$194.53	8.366%	$210.8044	$210.80	$210.80	$210.80
Purchase #3	$135.87	12.667%	$153.0807	$153.08	$153.10	$153.10
Purchase #4	$27.66	12.224%	$31.0412	$31.04	$31.05	$31.00
Purchase #5	$143.52	11.812%	$160.4726	$160.47	$160.45	$160.50
Purchase #6	$182.65	9.453%	$199.9159	$199.92	$199.90	$199.90
Purchase #7	$196.37	7.600%	$211.2941	$211.29	$211.30	$211.30
7 purchase totals =	$976.24		$1,066.5106	$1,066.50	$1,066.50	$1,066.50