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	$13.92	6.818%	$14.8691	$14.87	$14.85	$14.90
Purchase #2	$102.73	13.112%	$116.2	$116.20	$116.20	$116.20
Purchase #3	$244.47	13.838%	$278.2998	$278.30	$278.30	$278.30
Purchase #4	$36.50	10.263%	$40.246	$40.25	$40.25	$40.20
Purchase #5	$143.37	9.384%	$156.8238	$156.82	$156.80	$156.80
Purchase #6	$71.72	9.562%	$78.5779	$78.58	$78.60	$78.60
Purchase #7	$92.39	12.580%	$104.0127	$104.01	$104.00	$104.00
7 purchase totals =	$705.10		$789.0293	$789.03	$789.00	$789.00