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	$136.43	11.509%	$152.1317	$152.13	$152.15	$152.10
Purchase #2	$48.89	4.221%	$50.9536	$50.95	$50.95	$51.00
Purchase #3	$81.53	3.158%	$84.1047	$84.10	$84.10	$84.10
Purchase #4	$21.99	9.411%	$24.0595	$24.06	$24.05	$24.10
Purchase #5	$104.26	4.455%	$108.9048	$108.90	$108.90	$108.90
Purchase #6	$41.59	3.145%	$42.898	$42.90	$42.90	$42.90
Purchase #7	$35.76	4.596%	$37.4035	$37.40	$37.40	$37.40
7 purchase totals =	$470.45		$500.4558	$500.44	$500.45	$500.50