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	$240.58	9.644%	$263.7815	$263.78	$263.80	$263.80
Purchase #2	$49.37	12.183%	$55.3847	$55.38	$55.40	$55.40
Purchase #3	$136.45	3.743%	$141.5573	$141.56	$141.55	$141.60
Purchase #4	$93.94	6.486%	$100.0329	$100.03	$100.05	$100.00
Purchase #5	$35.76	3.688%	$37.0788	$37.08	$37.10	$37.10
Purchase #6	$146.41	7.157%	$156.8886	$156.89	$156.90	$156.90
Purchase #7	$177.70	7.358%	$190.7752	$190.78	$190.80	$190.80
7 purchase totals =	$880.21		$945.4990	$945.50	$945.60	$945.60