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	$65.34	6.391%	$69.5159	$69.52	$69.50	$69.50
Purchase #2	$223.47	12.262%	$250.8719	$250.87	$250.85	$250.90
Purchase #3	$217.91	7.256%	$233.7215	$233.72	$233.70	$233.70
Purchase #4	$132.85	8.191%	$143.7317	$143.73	$143.75	$143.70
Purchase #5	$31.75	12.844%	$35.828	$35.83	$35.85	$35.80
Purchase #6	$38.48	10.854%	$42.6566	$42.66	$42.65	$42.70
Purchase #7	$237.84	11.559%	$265.3319	$265.33	$265.35	$265.30
7 purchase totals =	$947.64		$1,041.6575	$1,041.66	$1,041.65	$1,041.60