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	$7.90	8.788%	$8.5943	$8.59	$8.60	$8.60
Purchase #2	$78.49	13.403%	$89.01	$89.01	$89.00	$89.00
Purchase #3	$62.48	12.556%	$70.325	$70.33	$70.35	$70.30
Purchase #4	$66.60	5.533%	$70.285	$70.29	$70.30	$70.30
Purchase #5	$206.83	13.498%	$234.7479	$234.75	$234.75	$234.70
Purchase #6	$51.46	12.127%	$57.7006	$57.70	$57.70	$57.70
Purchase #7	$52.85	5.368%	$55.687	$55.69	$55.70	$55.70
7 purchase totals =	$526.61		$586.3498	$586.36	$586.40	$586.30