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	$7.53	12.631%	$8.4811	$8.48	$8.50	$8.50
Purchase #2	$177.53	10.614%	$196.373	$196.37	$196.35	$196.40
Purchase #3	$99.71	4.583%	$104.2797	$104.28	$104.30	$104.30
Purchase #4	$190.84	12.488%	$214.6721	$214.67	$214.65	$214.70
Purchase #5	$166.72	9.513%	$182.5801	$182.58	$182.60	$182.60
Purchase #6	$58.50	13.774%	$66.5578	$66.56	$66.55	$66.60
Purchase #7	$81.82	5.653%	$86.4453	$86.45	$86.45	$86.40
7 purchase totals =	$782.65		$859.3891	$859.39	$859.40	$859.50