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	$211.32	8.555%	$229.3984	$229.40	$229.40	$229.40
Purchase #2	$245.89	13.411%	$278.8663	$278.87	$278.85	$278.90
Purchase #3	$100.69	3.683%	$104.3984	$104.40	$104.40	$104.40
Purchase #4	$122.29	12.195%	$137.2033	$137.20	$137.20	$137.20
Purchase #5	$58.30	6.577%	$62.1344	$62.13	$62.15	$62.10
Purchase #6	$243.69	7.742%	$262.5565	$262.56	$262.55	$262.60
Purchase #7	$135.84	12.354%	$152.6217	$152.62	$152.60	$152.60
7 purchase totals =	$1,118.02		$1,227.1790	$1,227.18	$1,227.15	$1,227.20