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	$106.33	10.531%	$117.5276	$117.53	$117.55	$117.50
Purchase #2	$232.39	11.564%	$259.2636	$259.26	$259.25	$259.30
Purchase #3	$90.52	10.508%	$100.0318	$100.03	$100.05	$100.00
Purchase #4	$90.27	9.731%	$99.0542	$99.05	$99.05	$99.10
Purchase #5	$209.60	10.535%	$231.6814	$231.68	$231.70	$231.70
Purchase #6	$125.89	11.819%	$140.7689	$140.77	$140.75	$140.80
Purchase #7	$73.25	11.209%	$81.4606	$81.46	$81.45	$81.50
7 purchase totals =	$928.25		$1,029.7881	$1,029.78	$1,029.80	$1,029.90