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	$19.95	5.606%	$21.0684	$21.07	$21.05	$21.10
Purchase #2	$54.46	12.706%	$61.3797	$61.38	$61.40	$61.40
Purchase #3	$243.58	13.542%	$276.5656	$276.57	$276.55	$276.60
Purchase #4	$111.57	11.602%	$124.5144	$124.51	$124.50	$124.50
Purchase #5	$162.78	11.396%	$181.3304	$181.33	$181.35	$181.30
Purchase #6	$201.68	10.493%	$222.8423	$222.84	$222.85	$222.80
Purchase #7	$189.58	10.695%	$209.8556	$209.86	$209.85	$209.90
7 purchase totals =	$983.60		$1,097.5564	$1,097.56	$1,097.55	$1,097.60