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	$38.42	3.198%	$39.6487	$39.65	$39.65	$39.60
Purchase #2	$136.41	11.801%	$152.5077	$152.51	$152.50	$152.50
Purchase #3	$68.78	12.799%	$77.5832	$77.58	$77.60	$77.60
Purchase #4	$221.97	3.565%	$229.8832	$229.88	$229.90	$229.90
Purchase #5	$100.67	3.241%	$103.9327	$103.93	$103.95	$103.90
Purchase #6	$131.52	10.738%	$145.6426	$145.64	$145.65	$145.60
Purchase #7	$80.50	8.668%	$87.4777	$87.48	$87.50	$87.50
7 purchase totals =	$778.27		$836.6758	$836.67	$836.75	$836.60