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	$25.36	7.666%	$27.3041	$27.30	$27.30	$27.30
Purchase #2	$41.32	3.660%	$42.8323	$42.83	$42.85	$42.80
Purchase #3	$175.96	12.759%	$198.4107	$198.41	$198.40	$198.40
Purchase #4	$148.86	12.587%	$167.597	$167.60	$167.60	$167.60
Purchase #5	$122.59	12.240%	$137.595	$137.60	$137.60	$137.60
Purchase #6	$137.31	10.832%	$152.1834	$152.18	$152.20	$152.20
Purchase #7	$88.31	13.226%	$99.9899	$99.99	$100.00	$100.00
7 purchase totals =	$739.71		$825.9124	$825.91	$825.95	$825.90