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	$131.31	8.748%	$142.797	$142.80	$142.80	$142.80
Purchase #2	$206.59	11.829%	$231.0275	$231.03	$231.05	$231.00
Purchase #3	$55.38	8.226%	$59.9356	$59.94	$59.95	$59.90
Purchase #4	$22.99	5.293%	$24.2069	$24.21	$24.20	$24.20
Purchase #5	$21.65	11.577%	$24.1564	$24.16	$24.15	$24.20
Purchase #6	$93.84	12.828%	$105.8778	$105.88	$105.90	$105.90
Purchase #7	$184.51	8.649%	$200.4683	$200.47	$200.45	$200.50
7 purchase totals =	$716.27		$788.4695	$788.49	$788.50	$788.50