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	$105.83	8.419%	$114.7398	$114.74	$114.75	$114.70
Purchase #2	$78.67	11.636%	$87.824	$87.82	$87.80	$87.80
Purchase #3	$162.86	6.168%	$172.9052	$172.91	$172.90	$172.90
Purchase #4	$99.62	3.804%	$103.4095	$103.41	$103.40	$103.40
Purchase #5	$24.61	3.440%	$25.4566	$25.46	$25.45	$25.50
Purchase #6	$130.89	10.471%	$144.5955	$144.60	$144.60	$144.60
Purchase #7	$116.63	12.302%	$130.9778	$130.98	$131.00	$131.00
7 purchase totals =	$719.11		$779.9084	$779.92	$779.90	$779.90