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	$131.56	6.233%	$139.7601	$139.76	$139.75	$139.80
Purchase #2	$70.89	5.191%	$74.5699	$74.57	$74.55	$74.60
Purchase #3	$38.35	10.804%	$42.4933	$42.49	$42.50	$42.50
Purchase #4	$78.34	12.459%	$88.1004	$88.10	$88.10	$88.10
Purchase #5	$153.59	13.224%	$173.9007	$173.90	$173.90	$173.90
Purchase #6	$63.57	3.516%	$65.8051	$65.81	$65.80	$65.80
Purchase #7	$136.54	12.596%	$153.7386	$153.74	$153.75	$153.70
7 purchase totals =	$672.84		$738.3681	$738.37	$738.35	$738.40