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	$244.98	6.324%	$260.4725	$260.47	$260.45	$260.50
Purchase #2	$131.81	4.179%	$137.3183	$137.32	$137.30	$137.30
Purchase #3	$189.81	5.750%	$200.7241	$200.72	$200.70	$200.70
Purchase #4	$31.29	13.507%	$35.5163	$35.52	$35.50	$35.50
Purchase #5	$46.32	3.411%	$47.9	$47.90	$47.90	$47.90
Purchase #6	$71.88	10.753%	$79.6093	$79.61	$79.60	$79.60
Purchase #7	$124.81	10.476%	$137.8851	$137.89	$137.90	$137.90
7 purchase totals =	$840.90		$899.4256	$899.43	$899.35	$899.40