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	$64.54	9.396%	$70.6042	$70.60	$70.60	$70.60
Purchase #2	$172.80	4.350%	$180.3168	$180.32	$180.30	$180.30
Purchase #3	$28.89	12.310%	$32.4464	$32.45	$32.45	$32.40
Purchase #4	$39.27	10.605%	$43.4346	$43.43	$43.45	$43.40
Purchase #5	$216.88	11.213%	$241.1988	$241.20	$241.20	$241.20
Purchase #6	$196.78	6.544%	$209.6573	$209.66	$209.65	$209.70
Purchase #7	$59.47	13.140%	$67.2844	$67.28	$67.30	$67.30
7 purchase totals =	$778.63		$844.9425	$844.94	$844.95	$844.90