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	$170.56	8.520%	$185.0917	$185.09	$185.10	$185.10
Purchase #2	$204.64	12.808%	$230.8503	$230.85	$230.85	$230.90
Purchase #3	$242.90	12.786%	$273.9572	$273.96	$273.95	$274.00
Purchase #4	$127.57	13.499%	$144.7907	$144.79	$144.80	$144.80
Purchase #5	$25.48	7.472%	$27.3839	$27.38	$27.40	$27.40
Purchase #6	$182.67	4.150%	$190.2508	$190.25	$190.25	$190.30
Purchase #7	$69.71	3.662%	$72.2628	$72.26	$72.25	$72.30
7 purchase totals =	$1,023.53		$1,124.5874	$1,124.58	$1,124.60	$1,124.80