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	$111.77	9.624%	$122.5267	$122.53	$122.55	$122.50
Purchase #2	$176.46	7.620%	$189.9063	$189.91	$189.90	$189.90
Purchase #3	$180.40	8.834%	$196.3365	$196.34	$196.35	$196.30
Purchase #4	$24.39	6.103%	$25.8785	$25.88	$25.90	$25.90
Purchase #5	$86.67	5.222%	$91.1959	$91.20	$91.20	$91.20
Purchase #6	$219.25	13.151%	$248.0836	$248.08	$248.10	$248.10
Purchase #7	$52.44	13.750%	$59.6505	$59.65	$59.65	$59.70
7 purchase totals =	$851.38		$933.5780	$933.59	$933.65	$933.60