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	$211.46	10.132%	$232.8851	$232.89	$232.90	$232.90
Purchase #2	$132.74	10.680%	$146.9166	$146.92	$146.90	$146.90
Purchase #3	$137.43	4.236%	$143.2515	$143.25	$143.25	$143.30
Purchase #4	$127.25	9.618%	$139.4889	$139.49	$139.50	$139.50
Purchase #5	$31.95	10.825%	$35.4086	$35.41	$35.40	$35.40
Purchase #6	$140.89	7.799%	$151.878	$151.88	$151.90	$151.90
Purchase #7	$58.50	12.221%	$65.6493	$65.65	$65.65	$65.60
7 purchase totals =	$840.22		$915.4780	$915.49	$915.50	$915.50