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	$242.77	9.791%	$266.5396	$266.54	$266.55	$266.50
Purchase #2	$41.32	8.337%	$44.7648	$44.76	$44.75	$44.80
Purchase #3	$145.33	13.690%	$165.2257	$165.23	$165.25	$165.20
Purchase #4	$237.63	7.530%	$255.5235	$255.52	$255.50	$255.50
Purchase #5	$141.55	10.843%	$156.8983	$156.90	$156.90	$156.90
Purchase #6	$72.81	4.249%	$75.9037	$75.90	$75.90	$75.90
Purchase #7	$138.27	10.448%	$152.7164	$152.72	$152.70	$152.70
7 purchase totals =	$1,019.68		$1,117.5720	$1,117.57	$1,117.55	$1,117.50