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	$146.63	13.665%	$166.667	$166.67	$166.65	$166.70
Purchase #2	$131.53	10.364%	$145.1618	$145.16	$145.15	$145.20
Purchase #3	$74.91	7.805%	$80.7567	$80.76	$80.75	$80.80
Purchase #4	$249.27	12.659%	$280.8251	$280.83	$280.85	$280.80
Purchase #5	$236.28	7.208%	$253.3111	$253.31	$253.30	$253.30
Purchase #6	$28.70	13.655%	$32.619	$32.62	$32.60	$32.60
Purchase #7	$200.74	9.253%	$219.3145	$219.31	$219.30	$219.30
7 purchase totals =	$1,068.06		$1,178.6552	$1,178.66	$1,178.60	$1,178.70