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	$30.68	3.666%	$31.8047	$31.80	$31.80	$31.80
Purchase #2	$155.80	5.449%	$164.2895	$164.29	$164.30	$164.30
Purchase #3	$42.81	5.115%	$44.9997	$45.00	$45.00	$45.00
Purchase #4	$46.63	9.158%	$50.9004	$50.90	$50.90	$50.90
Purchase #5	$46.48	11.723%	$51.9289	$51.93	$51.95	$51.90
Purchase #6	$144.42	10.720%	$159.9018	$159.90	$159.90	$159.90
Purchase #7	$193.52	3.381%	$200.0629	$200.06	$200.05	$200.10
7 purchase totals =	$660.34		$703.8879	$703.88	$703.90	$703.90