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	$150.40	7.317%	$161.4048	$161.40	$161.40	$161.40
Purchase #2	$234.63	9.195%	$256.2042	$256.20	$256.20	$256.20
Purchase #3	$214.70	12.668%	$241.8982	$241.90	$241.90	$241.90
Purchase #4	$100.34	11.511%	$111.8901	$111.89	$111.90	$111.90
Purchase #5	$84.46	6.697%	$90.1163	$90.12	$90.10	$90.10
Purchase #6	$36.69	3.722%	$38.0556	$38.06	$38.05	$38.10
Purchase #7	$144.84	10.460%	$159.9903	$159.99	$160.00	$160.00
7 purchase totals =	$966.06		$1,059.5595	$1,059.56	$1,059.55	$1,059.60