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	$55.91	12.728%	$63.0262	$63.03	$63.05	$63.00
Purchase #2	$150.84	9.121%	$164.5981	$164.60	$164.60	$164.60
Purchase #3	$112.71	9.384%	$123.2867	$123.29	$123.30	$123.30
Purchase #4	$55.96	6.764%	$59.7451	$59.75	$59.75	$59.70
Purchase #5	$54.41	10.187%	$59.9527	$59.95	$59.95	$60.00
Purchase #6	$70.63	8.609%	$76.7105	$76.71	$76.70	$76.70
Purchase #7	$43.75	10.612%	$48.3928	$48.39	$48.40	$48.40
7 purchase totals =	$544.21		$595.7121	$595.72	$595.75	$595.70