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	$97.35	11.478%	$108.5238	$108.52	$108.50	$108.50
Purchase #2	$168.80	6.345%	$179.5104	$179.51	$179.50	$179.50
Purchase #3	$114.94	10.666%	$127.1995	$127.20	$127.20	$127.20
Purchase #4	$237.82	12.696%	$268.0136	$268.01	$268.00	$268.00
Purchase #5	$79.55	12.479%	$89.477	$89.48	$89.50	$89.50
Purchase #6	$124.81	6.376%	$132.7679	$132.77	$132.75	$132.80
Purchase #7	$220.53	7.186%	$236.3773	$236.38	$236.40	$236.40
7 purchase totals =	$1,043.80		$1,141.8695	$1,141.87	$1,141.85	$1,141.90