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	$203.46	13.526%	$230.98	$230.98	$231.00	$231.00
Purchase #2	$242.29	6.711%	$258.5501	$258.55	$258.55	$258.60
Purchase #3	$119.96	6.410%	$127.6494	$127.65	$127.65	$127.60
Purchase #4	$81.95	13.255%	$92.8125	$92.81	$92.80	$92.80
Purchase #5	$129.28	6.437%	$137.6018	$137.60	$137.60	$137.60
Purchase #6	$195.54	11.838%	$218.688	$218.69	$218.70	$218.70
Purchase #7	$128.40	4.825%	$134.5953	$134.60	$134.60	$134.60
7 purchase totals =	$1,100.88		$1,200.8771	$1,200.88	$1,200.90	$1,200.90