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	$248.47	12.357%	$279.1734	$279.17	$279.15	$279.20
Purchase #2	$112.36	3.342%	$116.1151	$116.12	$116.10	$116.10
Purchase #3	$236.98	9.429%	$259.3248	$259.32	$259.30	$259.30
Purchase #4	$17.64	5.165%	$18.5511	$18.55	$18.55	$18.60
Purchase #5	$151.80	10.629%	$167.9348	$167.93	$167.95	$167.90
Purchase #6	$142.53	6.654%	$152.0139	$152.01	$152.00	$152.00
Purchase #7	$56.96	7.475%	$61.2178	$61.22	$61.20	$61.20
7 purchase totals =	$966.74		$1,054.3309	$1,054.32	$1,054.25	$1,054.30