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	$83.44	5.614%	$88.1243	$88.12	$88.10	$88.10
Purchase #2	$49.80	11.688%	$55.6206	$55.62	$55.60	$55.60
Purchase #3	$166.58	11.143%	$185.142	$185.14	$185.15	$185.10
Purchase #4	$25.63	9.628%	$28.0977	$28.10	$28.10	$28.10
Purchase #5	$137.99	12.658%	$155.4568	$155.46	$155.45	$155.50
Purchase #6	$52.40	13.596%	$59.5243	$59.52	$59.50	$59.50
Purchase #7	$104.80	8.592%	$113.8044	$113.80	$113.80	$113.80
7 purchase totals =	$620.64		$685.7701	$685.76	$685.70	$685.70