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	$124.63	3.414%	$128.8849	$128.88	$128.90	$128.90
Purchase #2	$160.77	4.817%	$168.5143	$168.51	$168.50	$168.50
Purchase #3	$51.39	3.260%	$53.0653	$53.07	$53.05	$53.10
Purchase #4	$44.26	5.480%	$46.6854	$46.69	$46.70	$46.70
Purchase #5	$199.38	9.529%	$218.3789	$218.38	$218.40	$218.40
Purchase #6	$228.28	8.592%	$247.8938	$247.89	$247.90	$247.90
Purchase #7	$33.33	6.451%	$35.4801	$35.48	$35.50	$35.50
7 purchase totals =	$842.04		$898.9027	$898.90	$898.95	$899.00