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	$17.88	13.320%	$20.2616	$20.26	$20.25	$20.30
Purchase #2	$169.98	5.833%	$179.8949	$179.89	$179.90	$179.90
Purchase #3	$60.48	11.839%	$67.6402	$67.64	$67.65	$67.60
Purchase #4	$230.89	12.157%	$258.9593	$258.96	$258.95	$259.00
Purchase #5	$143.82	6.780%	$153.571	$153.57	$153.55	$153.60
Purchase #6	$220.91	13.855%	$251.5171	$251.52	$251.50	$251.50
Purchase #7	$177.93	4.799%	$186.4689	$186.47	$186.45	$186.50
7 purchase totals =	$1,021.89		$1,118.3130	$1,118.31	$1,118.25	$1,118.40