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	$66.47	10.642%	$73.5437	$73.54	$73.55	$73.50
Purchase #2	$99.98	13.269%	$113.2463	$113.25	$113.25	$113.20
Purchase #3	$206.41	9.380%	$225.7713	$225.77	$225.75	$225.80
Purchase #4	$119.69	8.478%	$129.8373	$129.84	$129.85	$129.80
Purchase #5	$40.94	5.725%	$43.2838	$43.28	$43.30	$43.30
Purchase #6	$146.39	5.426%	$154.3331	$154.33	$154.35	$154.30
Purchase #7	$99.25	12.720%	$111.8746	$111.87	$111.85	$111.90
7 purchase totals =	$779.13		$851.8901	$851.88	$851.90	$851.80