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	$245.35	8.765%	$266.8549	$266.85	$266.85	$266.90
Purchase #2	$166.88	11.317%	$185.7658	$185.77	$185.75	$185.80
Purchase #3	$61.71	9.490%	$67.5663	$67.57	$67.55	$67.60
Purchase #4	$47.58	10.315%	$52.4879	$52.49	$52.50	$52.50
Purchase #5	$13.71	11.281%	$15.2566	$15.26	$15.25	$15.30
Purchase #6	$76.52	7.139%	$81.9828	$81.98	$82.00	$82.00
Purchase #7	$158.78	3.361%	$164.1166	$164.12	$164.10	$164.10
7 purchase totals =	$770.53		$834.0309	$834.04	$834.00	$834.20