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	$117.89	12.386%	$132.4919	$132.49	$132.50	$132.50
Purchase #2	$44.85	10.326%	$49.4812	$49.48	$49.50	$49.50
Purchase #3	$71.62	8.661%	$77.823	$77.82	$77.80	$77.80
Purchase #4	$239.69	5.854%	$253.7215	$253.72	$253.70	$253.70
Purchase #5	$72.83	10.407%	$80.4094	$80.41	$80.40	$80.40
Purchase #6	$157.70	13.690%	$179.2891	$179.29	$179.30	$179.30
Purchase #7	$67.75	12.691%	$76.3482	$76.35	$76.35	$76.30
7 purchase totals =	$772.33		$849.5643	$849.56	$849.55	$849.50