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	$11.68	9.402%	$12.7782	$12.78	$12.80	$12.80
Purchase #2	$190.89	11.772%	$213.3616	$213.36	$213.35	$213.40
Purchase #3	$148.97	13.509%	$169.0944	$169.09	$169.10	$169.10
Purchase #4	$117.43	5.122%	$123.4448	$123.44	$123.45	$123.40
Purchase #5	$57.92	6.803%	$61.8603	$61.86	$61.85	$61.90
Purchase #6	$225.28	3.157%	$232.3921	$232.39	$232.40	$232.40
Purchase #7	$171.45	10.383%	$189.2517	$189.25	$189.25	$189.30
7 purchase totals =	$923.62		$1,002.1831	$1,002.17	$1,002.20	$1,002.30