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	$148.79	7.867%	$160.4953	$160.50	$160.50	$160.50
Purchase #2	$91.36	9.308%	$99.8638	$99.86	$99.85	$99.90
Purchase #3	$67.65	6.802%	$72.2516	$72.25	$72.25	$72.30
Purchase #4	$131.89	5.405%	$139.0187	$139.02	$139.00	$139.00
Purchase #5	$210.48	4.469%	$219.8864	$219.89	$219.90	$219.90
Purchase #6	$22.28	10.277%	$24.5697	$24.57	$24.55	$24.60
Purchase #7	$148.26	4.174%	$154.4484	$154.45	$154.45	$154.40
7 purchase totals =	$820.71		$870.5339	$870.54	$870.50	$870.60