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	$7.55	12.179%	$8.4695	$8.47	$8.45	$8.50
Purchase #2	$57.59	7.382%	$61.8413	$61.84	$61.85	$61.80
Purchase #3	$177.34	9.361%	$193.9408	$193.94	$193.95	$193.90
Purchase #4	$109.76	7.490%	$117.981	$117.98	$118.00	$118.00
Purchase #5	$131.43	9.357%	$143.7279	$143.73	$143.75	$143.70
Purchase #6	$87.63	13.145%	$99.149	$99.15	$99.15	$99.10
Purchase #7	$78.84	13.460%	$89.4519	$89.45	$89.45	$89.50
7 purchase totals =	$650.14		$714.5614	$714.56	$714.60	$714.50