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	$106.48	6.496%	$113.3969	$113.40	$113.40	$113.40
Purchase #2	$94.27	6.834%	$100.7124	$100.71	$100.70	$100.70
Purchase #3	$171.62	10.679%	$189.9473	$189.95	$189.95	$189.90
Purchase #4	$95.43	10.442%	$105.3948	$105.39	$105.40	$105.40
Purchase #5	$123.80	4.851%	$129.8055	$129.81	$129.80	$129.80
Purchase #6	$119.93	3.171%	$123.733	$123.73	$123.75	$123.70
Purchase #7	$155.35	7.356%	$166.7775	$166.78	$166.80	$166.80
7 purchase totals =	$866.88		$929.7674	$929.77	$929.80	$929.70