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	$169.32	12.144%	$189.8822	$189.88	$189.90	$189.90
Purchase #2	$143.46	6.178%	$152.323	$152.32	$152.30	$152.30
Purchase #3	$225.83	6.385%	$240.2492	$240.25	$240.25	$240.20
Purchase #4	$151.85	8.634%	$164.9607	$164.96	$164.95	$165.00
Purchase #5	$57.89	5.773%	$61.232	$61.23	$61.25	$61.20
Purchase #6	$87.81	8.636%	$95.3933	$95.39	$95.40	$95.40
Purchase #7	$170.28	5.586%	$179.7918	$179.79	$179.80	$179.80
7 purchase totals =	$1,006.44		$1,083.8322	$1,083.82	$1,083.85	$1,083.80