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	$83.63	3.415%	$86.486	$86.49	$86.50	$86.50
Purchase #2	$143.83	5.741%	$152.0873	$152.09	$152.10	$152.10
Purchase #3	$141.98	5.761%	$150.1595	$150.16	$150.15	$150.20
Purchase #4	$35.28	9.474%	$38.6224	$38.62	$38.60	$38.60
Purchase #5	$69.40	13.547%	$78.8016	$78.80	$78.80	$78.80
Purchase #6	$44.78	5.548%	$47.2644	$47.26	$47.25	$47.30
Purchase #7	$109.46	10.256%	$120.6862	$120.69	$120.70	$120.70
7 purchase totals =	$628.36		$674.1074	$674.11	$674.10	$674.20