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	$118.41	6.849%	$126.5199	$126.52	$126.50	$126.50
Purchase #2	$241.94	9.363%	$264.5928	$264.59	$264.60	$264.60
Purchase #3	$19.48	12.322%	$21.8803	$21.88	$21.90	$21.90
Purchase #4	$247.99	12.273%	$278.4258	$278.43	$278.45	$278.40
Purchase #5	$38.56	7.830%	$41.5792	$41.58	$41.60	$41.60
Purchase #6	$210.49	5.583%	$222.2417	$222.24	$222.25	$222.20
Purchase #7	$25.68	9.223%	$28.0485	$28.05	$28.05	$28.00
7 purchase totals =	$902.55		$983.2882	$983.29	$983.35	$983.20