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	$229.47	4.861%	$240.6245	$240.62	$240.60	$240.60
Purchase #2	$129.70	12.444%	$145.8399	$145.84	$145.85	$145.80
Purchase #3	$155.91	9.734%	$171.0863	$171.09	$171.10	$171.10
Purchase #4	$86.25	5.281%	$90.8049	$90.80	$90.80	$90.80
Purchase #5	$69.67	12.171%	$78.1495	$78.15	$78.15	$78.10
Purchase #6	$218.81	3.121%	$225.6391	$225.64	$225.65	$225.60
Purchase #7	$232.30	3.506%	$240.4444	$240.44	$240.45	$240.40
7 purchase totals =	$1,122.11		$1,192.5886	$1,192.58	$1,192.60	$1,192.40