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	$15.45	5.846%	$16.3532	$16.35	$16.35	$16.40
Purchase #2	$163.39	9.833%	$179.4561	$179.46	$179.45	$179.50
Purchase #3	$203.39	8.783%	$221.2537	$221.25	$221.25	$221.30
Purchase #4	$45.26	12.375%	$50.8609	$50.86	$50.85	$50.90
Purchase #5	$191.28	4.804%	$200.4691	$200.47	$200.45	$200.50
Purchase #6	$168.81	12.284%	$189.5466	$189.55	$189.55	$189.50
Purchase #7	$191.37	13.247%	$216.7208	$216.72	$216.70	$216.70
7 purchase totals =	$978.95		$1,074.6604	$1,074.66	$1,074.60	$1,074.80