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	$73.72	5.857%	$78.0378	$78.04	$78.05	$78.00
Purchase #2	$136.53	10.666%	$151.0923	$151.09	$151.10	$151.10
Purchase #3	$246.85	7.588%	$265.581	$265.58	$265.60	$265.60
Purchase #4	$97.80	6.581%	$104.2362	$104.24	$104.25	$104.20
Purchase #5	$159.29	4.316%	$166.165	$166.17	$166.15	$166.20
Purchase #6	$107.69	3.404%	$111.3558	$111.36	$111.35	$111.40
Purchase #7	$35.60	9.433%	$38.9581	$38.96	$38.95	$39.00
7 purchase totals =	$857.48		$915.4262	$915.44	$915.45	$915.50