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	$28.87	7.789%	$31.1187	$31.12	$31.10	$31.10
Purchase #2	$86.33	4.476%	$90.1941	$90.19	$90.20	$90.20
Purchase #3	$220.71	7.301%	$236.824	$236.82	$236.80	$236.80
Purchase #4	$237.29	9.274%	$259.2963	$259.30	$259.30	$259.30
Purchase #5	$117.37	10.325%	$129.4885	$129.49	$129.50	$129.50
Purchase #6	$101.33	5.195%	$106.5941	$106.59	$106.60	$106.60
Purchase #7	$143.65	13.738%	$163.3846	$163.38	$163.40	$163.40
7 purchase totals =	$935.55		$1,016.9003	$1,016.89	$1,016.90	$1,016.90