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	$91.87	9.448%	$100.5499	$100.55	$100.55	$100.50
Purchase #2	$50.25	12.380%	$56.471	$56.47	$56.45	$56.50
Purchase #3	$173.51	4.832%	$181.894	$181.89	$181.90	$181.90
Purchase #4	$72.62	12.752%	$81.8805	$81.88	$81.90	$81.90
Purchase #5	$32.42	10.342%	$35.7729	$35.77	$35.75	$35.80
Purchase #6	$66.56	11.760%	$74.3875	$74.39	$74.40	$74.40
Purchase #7	$200.29	6.511%	$213.3309	$213.33	$213.35	$213.30
7 purchase totals =	$687.52		$744.2867	$744.28	$744.30	$744.30