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	$108.86	13.399%	$123.4462	$123.45	$123.45	$123.40
Purchase #2	$59.25	10.440%	$65.4357	$65.44	$65.45	$65.40
Purchase #3	$217.44	4.174%	$226.5159	$226.52	$226.50	$226.50
Purchase #4	$6.74	6.719%	$7.1929	$7.19	$7.20	$7.20
Purchase #5	$39.89	13.258%	$45.1786	$45.18	$45.20	$45.20
Purchase #6	$160.51	13.616%	$182.365	$182.37	$182.35	$182.40
Purchase #7	$166.81	8.623%	$181.194	$181.19	$181.20	$181.20
7 purchase totals =	$759.50		$831.3283	$831.34	$831.35	$831.30