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	$25.48	11.692%	$28.4591	$28.46	$28.45	$28.50
Purchase #2	$12.74	10.395%	$14.0643	$14.06	$14.05	$14.10
Purchase #3	$133.33	12.870%	$150.4896	$150.49	$150.50	$150.50
Purchase #4	$190.64	4.367%	$198.9652	$198.97	$198.95	$199.00
Purchase #5	$108.54	5.397%	$114.3979	$114.40	$114.40	$114.40
Purchase #6	$201.90	9.650%	$221.3834	$221.38	$221.40	$221.40
Purchase #7	$75.98	8.671%	$82.5682	$82.57	$82.55	$82.60
7 purchase totals =	$748.61		$810.3277	$810.33	$810.30	$810.50