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	$78.59	3.693%	$81.4923	$81.49	$81.50	$81.50
Purchase #2	$124.71	3.666%	$129.2819	$129.28	$129.30	$129.30
Purchase #3	$106.54	5.291%	$112.177	$112.18	$112.20	$112.20
Purchase #4	$53.60	10.327%	$59.1353	$59.14	$59.15	$59.10
Purchase #5	$89.25	12.737%	$100.6178	$100.62	$100.60	$100.60
Purchase #6	$221.68	11.338%	$246.8141	$246.81	$246.80	$246.80
Purchase #7	$186.38	5.344%	$196.3401	$196.34	$196.35	$196.30
7 purchase totals =	$860.75		$925.8585	$925.86	$925.90	$925.80