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	$34.95	7.402%	$37.537	$37.54	$37.55	$37.50
Purchase #2	$196.99	12.711%	$222.0294	$222.03	$222.05	$222.00
Purchase #3	$217.48	5.225%	$228.8433	$228.84	$228.85	$228.80
Purchase #4	$108.63	8.371%	$117.7234	$117.72	$117.70	$117.70
Purchase #5	$18.86	11.256%	$20.9829	$20.98	$21.00	$21.00
Purchase #6	$91.98	8.702%	$99.9841	$99.98	$100.00	$100.00
Purchase #7	$134.38	5.139%	$141.2858	$141.29	$141.30	$141.30
7 purchase totals =	$803.27		$868.3859	$868.38	$868.45	$868.30