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	$22.90	6.295%	$24.3416	$24.34	$24.35	$24.30
Purchase #2	$141.88	11.287%	$157.894	$157.89	$157.90	$157.90
Purchase #3	$69.53	4.158%	$72.4211	$72.42	$72.40	$72.40
Purchase #4	$200.37	10.708%	$221.8256	$221.83	$221.85	$221.80
Purchase #5	$155.33	4.763%	$162.7284	$162.73	$162.75	$162.70
Purchase #6	$149.36	13.202%	$169.0785	$169.08	$169.10	$169.10
Purchase #7	$81.39	10.778%	$90.1622	$90.16	$90.15	$90.20
7 purchase totals =	$820.76		$898.4514	$898.45	$898.50	$898.40