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	$65.89	7.357%	$70.7375	$70.74	$70.75	$70.70
Purchase #2	$155.36	11.239%	$172.8209	$172.82	$172.80	$172.80
Purchase #3	$152.42	10.811%	$168.8981	$168.90	$168.90	$168.90
Purchase #4	$91.71	4.475%	$95.814	$95.81	$95.80	$95.80
Purchase #5	$28.57	5.643%	$30.1822	$30.18	$30.20	$30.20
Purchase #6	$37.81	8.500%	$41.0239	$41.02	$41.00	$41.00
Purchase #7	$127.78	13.117%	$144.5409	$144.54	$144.55	$144.50
7 purchase totals =	$659.54		$724.0175	$724.01	$724.00	$723.90