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	$79.42	11.430%	$88.4977	$88.50	$88.50	$88.50
Purchase #2	$149.42	3.646%	$154.8679	$154.87	$154.85	$154.90
Purchase #3	$208.72	9.507%	$228.563	$228.56	$228.55	$228.60
Purchase #4	$165.57	12.166%	$185.7132	$185.71	$185.70	$185.70
Purchase #5	$150.45	5.308%	$158.4359	$158.44	$158.45	$158.40
Purchase #6	$164.92	8.276%	$178.5688	$178.57	$178.55	$178.60
Purchase #7	$42.59	5.546%	$44.952	$44.95	$44.95	$45.00
7 purchase totals =	$961.09		$1,039.5985	$1,039.60	$1,039.55	$1,039.70