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	$119.74	3.387%	$123.7956	$123.80	$123.80	$123.80
Purchase #2	$197.28	9.281%	$215.5896	$215.59	$215.60	$215.60
Purchase #3	$148.28	12.553%	$166.8936	$166.89	$166.90	$166.90
Purchase #4	$165.69	8.743%	$180.1763	$180.18	$180.20	$180.20
Purchase #5	$103.64	13.103%	$117.2199	$117.22	$117.20	$117.20
Purchase #6	$192.92	12.207%	$216.4697	$216.47	$216.45	$216.50
Purchase #7	$18.52	11.362%	$20.6242	$20.62	$20.60	$20.60
7 purchase totals =	$946.07		$1,040.7689	$1,040.77	$1,040.75	$1,040.80