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	$166.59	13.128%	$188.4599	$188.46	$188.45	$188.50
Purchase #2	$55.60	9.208%	$60.7196	$60.72	$60.70	$60.70
Purchase #3	$220.43	7.784%	$237.5883	$237.59	$237.60	$237.60
Purchase #4	$55.59	10.153%	$61.2341	$61.23	$61.25	$61.20
Purchase #5	$162.25	3.809%	$168.4301	$168.43	$168.45	$168.40
Purchase #6	$9.82	10.758%	$10.8764	$10.88	$10.90	$10.90
Purchase #7	$147.79	6.605%	$157.5515	$157.55	$157.55	$157.60
7 purchase totals =	$818.07		$884.8599	$884.86	$884.90	$884.90