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	$39.37	8.251%	$42.6184	$42.62	$42.60	$42.60
Purchase #2	$144.78	8.507%	$157.0964	$157.10	$157.10	$157.10
Purchase #3	$103.42	8.262%	$111.9646	$111.96	$111.95	$112.00
Purchase #4	$137.98	13.546%	$156.6708	$156.67	$156.65	$156.70
Purchase #5	$6.43	4.448%	$6.716	$6.72	$6.70	$6.70
Purchase #6	$74.80	10.827%	$82.8986	$82.90	$82.90	$82.90
Purchase #7	$221.78	5.448%	$233.8626	$233.86	$233.85	$233.90
7 purchase totals =	$728.56		$791.8274	$791.83	$791.75	$791.90