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	$8.93	13.189%	$10.1078	$10.11	$10.10	$10.10
Purchase #2	$27.28	3.462%	$28.2244	$28.22	$28.20	$28.20
Purchase #3	$196.55	5.268%	$206.9043	$206.90	$206.90	$206.90
Purchase #4	$63.39	12.111%	$71.0672	$71.07	$71.05	$71.10
Purchase #5	$163.55	5.497%	$172.5403	$172.54	$172.55	$172.50
Purchase #6	$101.58	8.544%	$110.259	$110.26	$110.25	$110.30
Purchase #7	$57.48	3.329%	$59.3935	$59.39	$59.40	$59.40
7 purchase totals =	$618.76		$658.4965	$658.49	$658.45	$658.50