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	$39.30	3.460%	$40.6598	$40.66	$40.65	$40.70
Purchase #2	$211.46	9.140%	$230.7874	$230.79	$230.80	$230.80
Purchase #3	$44.98	9.215%	$49.1249	$49.12	$49.10	$49.10
Purchase #4	$206.63	10.830%	$229.008	$229.01	$229.00	$229.00
Purchase #5	$89.37	12.344%	$100.4018	$100.40	$100.40	$100.40
Purchase #6	$92.61	7.107%	$99.1918	$99.19	$99.20	$99.20
Purchase #7	$171.94	10.777%	$190.47	$190.47	$190.45	$190.50
7 purchase totals =	$856.29		$939.6437	$939.64	$939.60	$939.70