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	$59.48	7.856%	$64.1527	$64.15	$64.15	$64.20
Purchase #2	$131.74	12.267%	$147.9005	$147.90	$147.90	$147.90
Purchase #3	$90.82	13.435%	$103.0217	$103.02	$103.00	$103.00
Purchase #4	$28.42	3.673%	$29.4639	$29.46	$29.45	$29.50
Purchase #5	$109.31	3.844%	$113.5119	$113.51	$113.50	$113.50
Purchase #6	$160.90	4.237%	$167.7173	$167.72	$167.70	$167.70
Purchase #7	$49.47	8.778%	$53.8125	$53.81	$53.80	$53.80
7 purchase totals =	$630.14		$679.5805	$679.57	$679.50	$679.60