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	$89.25	9.515%	$97.7421	$97.74	$97.75	$97.70
Purchase #2	$172.96	3.175%	$178.4515	$178.45	$178.45	$178.50
Purchase #3	$93.80	11.415%	$104.5073	$104.51	$104.50	$104.50
Purchase #4	$18.57	7.862%	$20.03	$20.03	$20.05	$20.00
Purchase #5	$93.78	7.448%	$100.7647	$100.76	$100.75	$100.80
Purchase #6	$36.79	5.847%	$38.9411	$38.94	$38.95	$38.90
Purchase #7	$180.81	9.710%	$198.3667	$198.37	$198.35	$198.40
7 purchase totals =	$685.96		$738.8034	$738.80	$738.80	$738.80