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	$77.96	5.847%	$82.5183	$82.52	$82.50	$82.50
Purchase #2	$106.77	12.781%	$120.4163	$120.42	$120.40	$120.40
Purchase #3	$247.90	13.173%	$280.5559	$280.56	$280.55	$280.60
Purchase #4	$101.60	12.368%	$114.1659	$114.17	$114.15	$114.20
Purchase #5	$152.36	9.513%	$166.854	$166.85	$166.85	$166.90
Purchase #6	$206.59	3.712%	$214.2586	$214.26	$214.25	$214.30
Purchase #7	$241.27	8.425%	$261.597	$261.60	$261.60	$261.60
7 purchase totals =	$1,134.45		$1,240.3660	$1,240.38	$1,240.30	$1,240.50