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	$64.37	9.478%	$70.471	$70.47	$70.45	$70.50
Purchase #2	$59.56	5.861%	$63.0508	$63.05	$63.05	$63.10
Purchase #3	$219.69	5.187%	$231.0853	$231.09	$231.10	$231.10
Purchase #4	$150.36	11.494%	$167.6424	$167.64	$167.65	$167.60
Purchase #5	$55.77	7.387%	$59.8897	$59.89	$59.90	$59.90
Purchase #6	$85.72	6.229%	$91.0595	$91.06	$91.05	$91.10
Purchase #7	$32.86	13.871%	$37.418	$37.42	$37.40	$37.40
7 purchase totals =	$668.33		$720.6167	$720.62	$720.60	$720.70