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	$90.54	10.770%	$100.2912	$100.29	$100.30	$100.30
Purchase #2	$149.59	11.162%	$166.2872	$166.29	$166.30	$166.30
Purchase #3	$216.92	4.820%	$227.3755	$227.38	$227.40	$227.40
Purchase #4	$170.44	5.874%	$180.4516	$180.45	$180.45	$180.50
Purchase #5	$50.89	4.105%	$52.979	$52.98	$53.00	$53.00
Purchase #6	$146.54	9.502%	$160.4642	$160.46	$160.45	$160.50
Purchase #7	$210.82	8.626%	$229.0053	$229.01	$229.00	$229.00
7 purchase totals =	$1,035.74		$1,116.8540	$1,116.86	$1,116.90	$1,117.00