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	$39.59	4.132%	$41.2259	$41.23	$41.25	$41.20
Purchase #2	$156.60	7.576%	$168.464	$168.46	$168.45	$168.50
Purchase #3	$207.26	8.304%	$224.4709	$224.47	$224.45	$224.50
Purchase #4	$248.76	11.856%	$278.253	$278.25	$278.25	$278.30
Purchase #5	$46.74	6.752%	$49.8959	$49.90	$49.90	$49.90
Purchase #6	$199.40	11.563%	$222.4566	$222.46	$222.45	$222.50
Purchase #7	$17.66	4.765%	$18.5015	$18.50	$18.50	$18.50
7 purchase totals =	$916.01		$1,003.2678	$1,003.27	$1,003.25	$1,003.40