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	$62.82	3.570%	$65.0627	$65.06	$65.05	$65.10
Purchase #2	$169.71	11.756%	$189.6611	$189.66	$189.65	$189.70
Purchase #3	$230.64	5.578%	$243.5051	$243.51	$243.50	$243.50
Purchase #4	$127.26	3.225%	$131.3641	$131.36	$131.35	$131.40
Purchase #5	$148.63	7.284%	$159.4562	$159.46	$159.45	$159.50
Purchase #6	$72.81	13.406%	$82.5709	$82.57	$82.55	$82.60
Purchase #7	$93.63	5.716%	$98.9819	$98.98	$99.00	$99.00
7 purchase totals =	$905.50		$970.6020	$970.60	$970.55	$970.80