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	$64.91	12.324%	$72.9095	$72.91	$72.90	$72.90
Purchase #2	$153.28	10.783%	$169.8082	$169.81	$169.80	$169.80
Purchase #3	$154.92	11.587%	$172.8706	$172.87	$172.85	$172.90
Purchase #4	$24.25	5.168%	$25.5032	$25.50	$25.50	$25.50
Purchase #5	$103.80	12.146%	$116.4075	$116.41	$116.40	$116.40
Purchase #6	$75.81	8.302%	$82.1037	$82.10	$82.10	$82.10
Purchase #7	$136.81	9.770%	$150.1763	$150.18	$150.20	$150.20
7 purchase totals =	$713.78		$789.7790	$789.78	$789.75	$789.80