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	$75.87	13.742%	$86.2961	$86.30	$86.30	$86.30
Purchase #2	$201.34	4.416%	$210.2312	$210.23	$210.25	$210.20
Purchase #3	$11.86	3.324%	$12.2542	$12.25	$12.25	$12.30
Purchase #4	$149.69	3.485%	$154.9067	$154.91	$154.90	$154.90
Purchase #5	$230.85	3.153%	$238.1287	$238.13	$238.15	$238.10
Purchase #6	$57.57	3.389%	$59.521	$59.52	$59.50	$59.50
Purchase #7	$211.82	4.749%	$221.8793	$221.88	$221.90	$221.90
7 purchase totals =	$939.00		$983.2172	$983.22	$983.25	$983.20