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	$139.38	3.450%	$144.1886	$144.19	$144.20	$144.20
Purchase #2	$39.90	5.846%	$42.2326	$42.23	$42.25	$42.20
Purchase #3	$39.60	13.427%	$44.9171	$44.92	$44.90	$44.90
Purchase #4	$154.69	12.260%	$173.655	$173.66	$173.65	$173.70
Purchase #5	$58.87	13.382%	$66.748	$66.75	$66.75	$66.70
Purchase #6	$96.48	13.436%	$109.4431	$109.44	$109.45	$109.40
Purchase #7	$14.32	10.667%	$15.8475	$15.85	$15.85	$15.80
7 purchase totals =	$543.24		$597.0319	$597.04	$597.05	$596.90