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	$47.79	7.579%	$51.412	$51.41	$51.40	$51.40
Purchase #2	$158.33	4.853%	$166.0138	$166.01	$166.00	$166.00
Purchase #3	$34.69	7.825%	$37.4045	$37.40	$37.40	$37.40
Purchase #4	$29.27	9.472%	$32.0425	$32.04	$32.05	$32.00
Purchase #5	$76.37	8.288%	$82.6995	$82.70	$82.70	$82.70
Purchase #6	$189.55	12.576%	$213.3878	$213.39	$213.40	$213.40
Purchase #7	$19.85	13.380%	$22.5059	$22.51	$22.50	$22.50
7 purchase totals =	$555.85		$605.4660	$605.46	$605.45	$605.40