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	$108.44	7.481%	$116.5524	$116.55	$116.55	$116.60
Purchase #2	$98.64	11.422%	$109.9067	$109.91	$109.90	$109.90
Purchase #3	$152.34	12.660%	$171.6262	$171.63	$171.65	$171.60
Purchase #4	$148.30	12.320%	$166.5706	$166.57	$166.55	$166.60
Purchase #5	$212.59	9.784%	$233.3898	$233.39	$233.40	$233.40
Purchase #6	$116.68	12.688%	$131.4844	$131.48	$131.50	$131.50
Purchase #7	$61.56	11.705%	$68.7656	$68.77	$68.75	$68.80
7 purchase totals =	$898.55		$998.2957	$998.30	$998.30	$998.40