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	$6.58	8.609%	$7.1465	$7.15	$7.15	$7.10
Purchase #2	$160.54	3.102%	$165.52	$165.52	$165.50	$165.50
Purchase #3	$34.50	9.636%	$37.8244	$37.82	$37.80	$37.80
Purchase #4	$153.58	8.795%	$167.0874	$167.09	$167.10	$167.10
Purchase #5	$136.66	11.763%	$152.7353	$152.74	$152.75	$152.70
Purchase #6	$13.58	6.527%	$14.4664	$14.47	$14.45	$14.50
Purchase #7	$215.31	7.709%	$231.9082	$231.91	$231.90	$231.90
7 purchase totals =	$720.75		$776.6882	$776.70	$776.65	$776.60