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	$36.72	9.340%	$40.1496	$40.15	$40.15	$40.10
Purchase #2	$204.39	3.468%	$211.4782	$211.48	$211.50	$211.50
Purchase #3	$132.58	3.257%	$136.8981	$136.90	$136.90	$136.90
Purchase #4	$72.98	8.131%	$78.914	$78.91	$78.90	$78.90
Purchase #5	$119.38	10.597%	$132.0307	$132.03	$132.05	$132.00
Purchase #6	$68.90	8.747%	$74.9267	$74.93	$74.95	$74.90
Purchase #7	$33.89	12.470%	$38.1161	$38.12	$38.10	$38.10
7 purchase totals =	$668.84		$712.5134	$712.52	$712.55	$712.40