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	$11.92	8.389%	$12.92	$12.92	$12.90	$12.90
Purchase #2	$85.72	4.601%	$89.664	$89.66	$89.65	$89.70
Purchase #3	$23.47	10.126%	$25.8466	$25.85	$25.85	$25.80
Purchase #4	$73.94	11.552%	$82.4815	$82.48	$82.50	$82.50
Purchase #5	$97.39	4.586%	$101.8563	$101.86	$101.85	$101.90
Purchase #6	$164.55	3.461%	$170.2451	$170.25	$170.25	$170.20
Purchase #7	$96.36	8.535%	$104.5843	$104.58	$104.60	$104.60
7 purchase totals =	$553.35		$587.5978	$587.60	$587.60	$587.60