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	$5.51	12.661%	$6.2076	$6.21	$6.20	$6.20
Purchase #2	$143.70	5.833%	$152.082	$152.08	$152.10	$152.10
Purchase #3	$82.67	5.138%	$86.9176	$86.92	$86.90	$86.90
Purchase #4	$80.62	12.349%	$90.5758	$90.58	$90.60	$90.60
Purchase #5	$27.80	4.412%	$29.0265	$29.03	$29.05	$29.00
Purchase #6	$28.76	10.544%	$31.7925	$31.79	$31.80	$31.80
Purchase #7	$131.54	4.692%	$137.7119	$137.71	$137.70	$137.70
7 purchase totals =	$500.60		$534.3139	$534.32	$534.35	$534.30