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	$17.44	8.151%	$18.8615	$18.86	$18.85	$18.90
Purchase #2	$20.80	8.218%	$22.5093	$22.51	$22.50	$22.50
Purchase #3	$188.70	5.380%	$198.8521	$198.85	$198.85	$198.90
Purchase #4	$109.82	5.836%	$116.2291	$116.23	$116.25	$116.20
Purchase #5	$228.56	13.717%	$259.9116	$259.91	$259.90	$259.90
Purchase #6	$28.58	3.488%	$29.5769	$29.58	$29.60	$29.60
Purchase #7	$145.73	7.260%	$156.31	$156.31	$156.30	$156.30
7 purchase totals =	$739.63		$802.2505	$802.25	$802.25	$802.30