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	$166.77	10.684%	$184.5877	$184.59	$184.60	$184.60
Purchase #2	$135.77	12.646%	$152.9395	$152.94	$152.95	$152.90
Purchase #3	$57.52	13.592%	$65.3381	$65.34	$65.35	$65.30
Purchase #4	$5.63	9.405%	$6.1595	$6.16	$6.15	$6.20
Purchase #5	$57.43	4.147%	$59.8116	$59.81	$59.80	$59.80
Purchase #6	$160.39	8.503%	$174.028	$174.03	$174.05	$174.00
Purchase #7	$44.57	6.814%	$47.607	$47.61	$47.60	$47.60
7 purchase totals =	$628.08		$690.4714	$690.48	$690.50	$690.40