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	$41.40	3.397%	$42.8064	$42.81	$42.80	$42.80
Purchase #2	$61.86	7.354%	$66.4092	$66.41	$66.40	$66.40
Purchase #3	$136.52	4.358%	$142.4695	$142.47	$142.45	$142.50
Purchase #4	$230.25	7.729%	$248.046	$248.05	$248.05	$248.00
Purchase #5	$53.43	11.439%	$59.5419	$59.54	$59.55	$59.50
Purchase #6	$131.81	5.237%	$138.7129	$138.71	$138.70	$138.70
Purchase #7	$131.68	9.373%	$144.0224	$144.02	$144.00	$144.00
7 purchase totals =	$786.95		$842.0083	$842.01	$841.95	$841.90