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	$145.47	6.642%	$155.1321	$155.13	$155.15	$155.10
Purchase #2	$65.64	11.114%	$72.9352	$72.94	$72.95	$72.90
Purchase #3	$130.39	5.261%	$137.2498	$137.25	$137.25	$137.20
Purchase #4	$245.59	13.179%	$277.9563	$277.96	$277.95	$278.00
Purchase #5	$186.72	9.752%	$204.9289	$204.93	$204.95	$204.90
Purchase #6	$172.78	8.204%	$186.9549	$186.95	$186.95	$187.00
Purchase #7	$129.25	6.367%	$137.4793	$137.48	$137.50	$137.50
7 purchase totals =	$1,075.84		$1,172.6365	$1,172.64	$1,172.70	$1,172.60