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	$50.33	9.257%	$54.989	$54.99	$55.00	$55.00
Purchase #2	$169.31	12.484%	$190.4467	$190.45	$190.45	$190.40
Purchase #3	$182.65	5.384%	$192.4839	$192.48	$192.50	$192.50
Purchase #4	$124.55	5.214%	$131.044	$131.04	$131.05	$131.00
Purchase #5	$120.70	13.281%	$136.7302	$136.73	$136.75	$136.70
Purchase #6	$118.92	13.173%	$134.5853	$134.59	$134.60	$134.60
Purchase #7	$164.52	7.113%	$176.2223	$176.22	$176.20	$176.20
7 purchase totals =	$930.98		$1,016.5014	$1,016.50	$1,016.55	$1,016.40