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	$122.66	6.871%	$131.088	$131.09	$131.10	$131.10
Purchase #2	$140.96	8.688%	$153.2066	$153.21	$153.20	$153.20
Purchase #3	$112.29	13.711%	$127.6861	$127.69	$127.70	$127.70
Purchase #4	$39.67	7.164%	$42.512	$42.51	$42.50	$42.50
Purchase #5	$12.96	10.839%	$14.3647	$14.36	$14.35	$14.40
Purchase #6	$244.26	5.729%	$258.2537	$258.25	$258.25	$258.30
Purchase #7	$79.68	9.645%	$87.3651	$87.37	$87.35	$87.40
7 purchase totals =	$752.48		$814.4762	$814.48	$814.45	$814.60