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	$5.38	13.595%	$6.1114	$6.11	$6.10	$6.10
Purchase #2	$156.75	4.327%	$163.5326	$163.53	$163.55	$163.50
Purchase #3	$50.90	4.527%	$53.2042	$53.20	$53.20	$53.20
Purchase #4	$63.63	10.179%	$70.1069	$70.11	$70.10	$70.10
Purchase #5	$37.38	13.366%	$42.3762	$42.38	$42.40	$42.40
Purchase #6	$214.72	4.804%	$225.0351	$225.04	$225.05	$225.00
Purchase #7	$86.38	3.713%	$89.5873	$89.59	$89.60	$89.60
7 purchase totals =	$615.14		$649.9537	$649.96	$650.00	$649.90