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	$80.45	6.116%	$85.3703	$85.37	$85.35	$85.40
Purchase #2	$119.45	3.644%	$123.8028	$123.80	$123.80	$123.80
Purchase #3	$103.37	8.786%	$112.4521	$112.45	$112.45	$112.50
Purchase #4	$194.26	8.163%	$210.1174	$210.12	$210.10	$210.10
Purchase #5	$229.62	10.480%	$253.6842	$253.68	$253.70	$253.70
Purchase #6	$100.90	10.196%	$111.1878	$111.19	$111.20	$111.20
Purchase #7	$218.80	7.466%	$235.1356	$235.14	$235.15	$235.10
7 purchase totals =	$1,046.85		$1,131.7502	$1,131.75	$1,131.75	$1,131.80