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	$126.49	10.194%	$139.3844	$139.38	$139.40	$139.40
Purchase #2	$27.90	4.729%	$29.2194	$29.22	$29.20	$29.20
Purchase #3	$83.86	12.357%	$94.2226	$94.22	$94.20	$94.20
Purchase #4	$69.66	13.601%	$79.1345	$79.13	$79.15	$79.10
Purchase #5	$83.88	7.874%	$90.4847	$90.48	$90.50	$90.50
Purchase #6	$95.80	6.189%	$101.7291	$101.73	$101.75	$101.70
Purchase #7	$96.71	4.303%	$100.8714	$100.87	$100.85	$100.90
7 purchase totals =	$584.30		$635.0461	$635.03	$635.05	$635.00