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	$78.99	8.559%	$85.7508	$85.75	$85.75	$85.80
Purchase #2	$160.81	7.328%	$172.5942	$172.59	$172.60	$172.60
Purchase #3	$37.30	11.245%	$41.4944	$41.49	$41.50	$41.50
Purchase #4	$147.33	3.228%	$152.0858	$152.09	$152.10	$152.10
Purchase #5	$30.28	3.156%	$31.2356	$31.24	$31.25	$31.20
Purchase #6	$119.28	12.678%	$134.4023	$134.40	$134.40	$134.40
Purchase #7	$46.32	13.277%	$52.4699	$52.47	$52.45	$52.50
7 purchase totals =	$620.31		$670.0330	$670.03	$670.05	$670.10