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	$7.71	11.142%	$8.569	$8.57	$8.55	$8.60
Purchase #2	$51.90	6.172%	$55.1033	$55.10	$55.10	$55.10
Purchase #3	$34.79	3.313%	$35.9426	$35.94	$35.95	$35.90
Purchase #4	$37.92	10.850%	$42.0343	$42.03	$42.05	$42.00
Purchase #5	$21.33	10.289%	$23.5246	$23.52	$23.50	$23.50
Purchase #6	$92.88	11.526%	$103.5853	$103.59	$103.60	$103.60
Purchase #7	$245.87	4.589%	$257.153	$257.15	$257.15	$257.20
7 purchase totals =	$492.40		$525.9121	$525.90	$525.90	$525.90