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	$54.61	11.292%	$60.7766	$60.78	$60.80	$60.80
Purchase #2	$74.47	11.831%	$83.2805	$83.28	$83.30	$83.30
Purchase #3	$99.90	6.380%	$106.2736	$106.27	$106.25	$106.30
Purchase #4	$148.61	6.843%	$158.7794	$158.78	$158.80	$158.80
Purchase #5	$249.59	9.427%	$273.1188	$273.12	$273.10	$273.10
Purchase #6	$131.43	11.527%	$146.5799	$146.58	$146.60	$146.60
Purchase #7	$164.62	5.115%	$173.0403	$173.04	$173.05	$173.00
7 purchase totals =	$923.23		$1,001.8491	$1,001.85	$1,001.90	$1,001.90