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	$217.29	6.718%	$231.8875	$231.89	$231.90	$231.90
Purchase #2	$92.67	11.368%	$103.2047	$103.20	$103.20	$103.20
Purchase #3	$227.31	8.126%	$245.7812	$245.78	$245.80	$245.80
Purchase #4	$244.32	5.647%	$258.1168	$258.12	$258.10	$258.10
Purchase #5	$90.43	8.150%	$97.8	$97.80	$97.80	$97.80
Purchase #6	$116.91	5.384%	$123.2044	$123.20	$123.20	$123.20
Purchase #7	$107.92	4.629%	$112.9156	$112.92	$112.90	$112.90
7 purchase totals =	$1,096.85		$1,172.9102	$1,172.91	$1,172.90	$1,172.90