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	$11.26	13.349%	$12.7631	$12.76	$12.75	$12.80
Purchase #2	$107.47	5.307%	$113.1734	$113.17	$113.15	$113.20
Purchase #3	$66.25	9.825%	$72.7591	$72.76	$72.75	$72.80
Purchase #4	$160.56	7.848%	$173.1607	$173.16	$173.15	$173.20
Purchase #5	$125.80	12.475%	$141.4936	$141.49	$141.50	$141.50
Purchase #6	$95.90	7.559%	$103.1491	$103.15	$103.15	$103.10
Purchase #7	$145.94	4.223%	$152.103	$152.10	$152.10	$152.10
7 purchase totals =	$713.18		$768.6020	$768.59	$768.55	$768.70