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	$38.48	10.865%	$42.6609	$42.66	$42.65	$42.70
Purchase #2	$29.31	7.334%	$31.4596	$31.46	$31.45	$31.50
Purchase #3	$145.25	6.569%	$154.7915	$154.79	$154.80	$154.80
Purchase #4	$144.66	11.538%	$161.3509	$161.35	$161.35	$161.40
Purchase #5	$20.48	5.410%	$21.588	$21.59	$21.60	$21.60
Purchase #6	$120.74	5.755%	$127.6886	$127.69	$127.70	$127.70
Purchase #7	$108.90	12.871%	$122.9165	$122.92	$122.90	$122.90
7 purchase totals =	$607.82		$662.4560	$662.46	$662.45	$662.60