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	$75.60	6.824%	$80.7589	$80.76	$80.75	$80.80
Purchase #2	$107.67	3.444%	$111.3782	$111.38	$111.40	$111.40
Purchase #3	$82.82	6.646%	$88.3242	$88.32	$88.30	$88.30
Purchase #4	$134.27	7.868%	$144.8344	$144.83	$144.85	$144.80
Purchase #5	$73.79	10.382%	$81.4509	$81.45	$81.45	$81.50
Purchase #6	$72.55	3.122%	$74.815	$74.82	$74.80	$74.80
Purchase #7	$120.89	7.319%	$129.7379	$129.74	$129.75	$129.70
7 purchase totals =	$667.59		$711.2995	$711.30	$711.30	$711.30