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	$76.69	4.445%	$80.0989	$80.10	$80.10	$80.10
Purchase #2	$46.80	11.411%	$52.1403	$52.14	$52.15	$52.10
Purchase #3	$204.88	6.614%	$218.4308	$218.43	$218.45	$218.40
Purchase #4	$157.35	8.661%	$170.9781	$170.98	$171.00	$171.00
Purchase #5	$109.56	8.291%	$118.6436	$118.64	$118.65	$118.60
Purchase #6	$42.29	7.603%	$45.5053	$45.51	$45.50	$45.50
Purchase #7	$199.56	11.587%	$222.683	$222.68	$222.70	$222.70
7 purchase totals =	$837.13		$908.4800	$908.48	$908.55	$908.40