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	$138.59	6.469%	$147.5554	$147.56	$147.55	$147.60
Purchase #2	$66.89	5.325%	$70.4519	$70.45	$70.45	$70.50
Purchase #3	$172.30	4.125%	$179.4074	$179.41	$179.40	$179.40
Purchase #4	$128.98	8.574%	$140.0387	$140.04	$140.05	$140.00
Purchase #5	$247.48	4.830%	$259.4333	$259.43	$259.45	$259.40
Purchase #6	$42.83	3.368%	$44.2725	$44.27	$44.25	$44.30
Purchase #7	$134.80	5.815%	$142.6386	$142.64	$142.65	$142.60
7 purchase totals =	$931.87		$983.7978	$983.80	$983.80	$983.80