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	$91.78	10.579%	$101.4894	$101.49	$101.50	$101.50
Purchase #2	$211.75	5.255%	$222.8775	$222.88	$222.90	$222.90
Purchase #3	$150.76	13.246%	$170.7297	$170.73	$170.75	$170.70
Purchase #4	$16.86	8.809%	$18.3452	$18.35	$18.35	$18.30
Purchase #5	$54.81	5.508%	$57.8289	$57.83	$57.85	$57.80
Purchase #6	$118.33	5.242%	$124.5329	$124.53	$124.55	$124.50
Purchase #7	$119.37	9.822%	$131.0945	$131.09	$131.10	$131.10
7 purchase totals =	$763.66		$826.8981	$826.90	$827.00	$826.80