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	$33.92	9.779%	$37.237	$37.24	$37.25	$37.20
Purchase #2	$129.43	7.259%	$138.8253	$138.83	$138.85	$138.80
Purchase #3	$117.25	8.851%	$127.6278	$127.63	$127.65	$127.60
Purchase #4	$201.58	8.831%	$219.3815	$219.38	$219.40	$219.40
Purchase #5	$200.86	10.538%	$222.0266	$222.03	$222.05	$222.00
Purchase #6	$132.48	3.345%	$136.9115	$136.91	$136.90	$136.90
Purchase #7	$71.58	3.178%	$73.8548	$73.85	$73.85	$73.90
7 purchase totals =	$887.10		$955.8645	$955.87	$955.95	$955.80