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	$104.86	8.269%	$113.5309	$113.53	$113.55	$113.50
Purchase #2	$112.25	9.730%	$123.1719	$123.17	$123.15	$123.20
Purchase #3	$139.52	11.600%	$155.7043	$155.70	$155.70	$155.70
Purchase #4	$117.46	10.804%	$130.1504	$130.15	$130.15	$130.20
Purchase #5	$197.95	4.251%	$206.3649	$206.36	$206.35	$206.40
Purchase #6	$138.66	10.441%	$153.1375	$153.14	$153.15	$153.10
Purchase #7	$53.45	10.623%	$59.128	$59.13	$59.15	$59.10
7 purchase totals =	$864.15		$941.1879	$941.18	$941.20	$941.20