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	$142.88	10.189%	$157.438	$157.44	$157.45	$157.40
Purchase #2	$134.26	11.771%	$150.0637	$150.06	$150.05	$150.10
Purchase #3	$53.56	11.160%	$59.5373	$59.54	$59.55	$59.50
Purchase #4	$56.62	7.638%	$60.9446	$60.94	$60.95	$60.90
Purchase #5	$80.46	7.496%	$86.4913	$86.49	$86.50	$86.50
Purchase #6	$88.59	11.783%	$99.0286	$99.03	$99.05	$99.00
Purchase #7	$245.49	4.778%	$257.2195	$257.22	$257.20	$257.20
7 purchase totals =	$801.86		$870.7230	$870.72	$870.75	$870.60