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	$76.71	4.727%	$80.3361	$80.34	$80.35	$80.30
Purchase #2	$185.68	7.351%	$199.3293	$199.33	$199.35	$199.30
Purchase #3	$236.98	7.874%	$255.6398	$255.64	$255.65	$255.60
Purchase #4	$128.47	9.660%	$140.8802	$140.88	$140.90	$140.90
Purchase #5	$32.60	5.251%	$34.3118	$34.31	$34.30	$34.30
Purchase #6	$41.81	9.757%	$45.8894	$45.89	$45.90	$45.90
Purchase #7	$163.76	12.571%	$184.3463	$184.35	$184.35	$184.30
7 purchase totals =	$866.01		$940.7329	$940.74	$940.80	$940.60