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	$13.42	6.387%	$14.2771	$14.28	$14.30	$14.30
Purchase #2	$84.77	13.174%	$95.9376	$95.94	$95.95	$95.90
Purchase #3	$135.26	7.432%	$145.3125	$145.31	$145.30	$145.30
Purchase #4	$84.66	5.332%	$89.1741	$89.17	$89.15	$89.20
Purchase #5	$131.75	4.310%	$137.4284	$137.43	$137.45	$137.40
Purchase #6	$54.51	3.133%	$56.2178	$56.22	$56.20	$56.20
Purchase #7	$142.69	8.739%	$155.1597	$155.16	$155.15	$155.20
7 purchase totals =	$647.06		$693.5072	$693.51	$693.50	$693.50