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	$113.63	8.684%	$123.4976	$123.50	$123.50	$123.50
Purchase #2	$31.69	12.295%	$35.5863	$35.59	$35.60	$35.60
Purchase #3	$48.54	6.347%	$51.6208	$51.62	$51.60	$51.60
Purchase #4	$107.59	13.758%	$122.3922	$122.39	$122.40	$122.40
Purchase #5	$47.98	6.601%	$51.1472	$51.15	$51.15	$51.10
Purchase #6	$50.39	11.730%	$56.3007	$56.30	$56.30	$56.30
Purchase #7	$67.85	12.447%	$76.2953	$76.30	$76.30	$76.30
7 purchase totals =	$467.67		$516.8401	$516.85	$516.85	$516.80