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	$43.90	11.386%	$48.8985	$48.90	$48.90	$48.90
Purchase #2	$130.88	8.866%	$142.4838	$142.48	$142.50	$142.50
Purchase #3	$249.44	11.285%	$277.5893	$277.59	$277.60	$277.60
Purchase #4	$34.65	3.322%	$35.8011	$35.80	$35.80	$35.80
Purchase #5	$41.28	13.249%	$46.7492	$46.75	$46.75	$46.70
Purchase #6	$209.53	6.667%	$223.4994	$223.50	$223.50	$223.50
Purchase #7	$46.73	10.781%	$51.768	$51.77	$51.75	$51.80
7 purchase totals =	$756.41		$826.7893	$826.79	$826.80	$826.80