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	$52.59	6.854%	$56.1945	$56.19	$56.20	$56.20
Purchase #2	$131.58	8.565%	$142.8498	$142.85	$142.85	$142.80
Purchase #3	$172.65	9.237%	$188.5977	$188.60	$188.60	$188.60
Purchase #4	$54.43	13.641%	$61.8548	$61.85	$61.85	$61.90
Purchase #5	$193.46	12.740%	$218.1068	$218.11	$218.10	$218.10
Purchase #6	$152.93	12.511%	$172.0631	$172.06	$172.05	$172.10
Purchase #7	$246.78	10.766%	$273.3483	$273.35	$273.35	$273.30
7 purchase totals =	$1,004.42		$1,113.0150	$1,113.01	$1,113.00	$1,113.00