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	$10.61	11.827%	$11.8648	$11.86	$11.85	$11.90
Purchase #2	$52.96	12.118%	$59.3777	$59.38	$59.40	$59.40
Purchase #3	$58.84	12.117%	$65.9696	$65.97	$65.95	$66.00
Purchase #4	$141.70	13.546%	$160.8947	$160.89	$160.90	$160.90
Purchase #5	$240.54	3.558%	$249.0984	$249.10	$249.10	$249.10
Purchase #6	$98.87	4.155%	$102.978	$102.98	$103.00	$103.00
Purchase #7	$229.96	5.276%	$242.0927	$242.09	$242.10	$242.10
7 purchase totals =	$833.48		$892.2759	$892.27	$892.30	$892.40