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	$29.72	6.410%	$31.6251	$31.63	$31.65	$31.60
Purchase #2	$38.52	9.307%	$42.1051	$42.11	$42.10	$42.10
Purchase #3	$34.27	6.839%	$36.6137	$36.61	$36.60	$36.60
Purchase #4	$89.53	10.741%	$99.1464	$99.15	$99.15	$99.10
Purchase #5	$76.95	5.187%	$80.9414	$80.94	$80.95	$80.90
Purchase #6	$164.62	7.475%	$176.9253	$176.93	$176.95	$176.90
Purchase #7	$43.28	3.216%	$44.6719	$44.67	$44.65	$44.70
7 purchase totals =	$476.89		$512.0289	$512.04	$512.05	$511.90