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	$210.43	4.874%	$220.6864	$220.69	$220.70	$220.70
Purchase #2	$229.64	13.167%	$259.8767	$259.88	$259.90	$259.90
Purchase #3	$145.65	11.848%	$162.9066	$162.91	$162.90	$162.90
Purchase #4	$181.65	8.169%	$196.489	$196.49	$196.50	$196.50
Purchase #5	$43.80	12.470%	$49.2619	$49.26	$49.25	$49.30
Purchase #6	$83.34	5.471%	$87.8995	$87.90	$87.90	$87.90
Purchase #7	$105.84	7.604%	$113.8881	$113.89	$113.90	$113.90
7 purchase totals =	$1,000.35		$1,091.0082	$1,091.02	$1,091.05	$1,091.10