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	$84.45	8.536%	$91.6587	$91.66	$91.65	$91.70
Purchase #2	$161.69	3.123%	$166.7396	$166.74	$166.75	$166.70
Purchase #3	$148.30	12.281%	$166.5127	$166.51	$166.50	$166.50
Purchase #4	$168.31	10.330%	$185.6964	$185.70	$185.70	$185.70
Purchase #5	$125.67	9.689%	$137.8462	$137.85	$137.85	$137.80
Purchase #6	$145.51	7.563%	$156.5149	$156.51	$156.50	$156.50
Purchase #7	$200.60	13.651%	$227.9839	$227.98	$228.00	$228.00
7 purchase totals =	$1,034.53		$1,132.9524	$1,132.95	$1,132.95	$1,132.90