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	$145.96	12.482%	$164.1787	$164.18	$164.20	$164.20
Purchase #2	$38.90	4.719%	$40.7357	$40.74	$40.75	$40.70
Purchase #3	$116.90	9.808%	$128.3656	$128.37	$128.35	$128.40
Purchase #4	$200.66	13.757%	$228.2648	$228.26	$228.25	$228.30
Purchase #5	$250.51	10.337%	$276.4052	$276.41	$276.40	$276.40
Purchase #6	$75.75	9.451%	$82.9091	$82.91	$82.90	$82.90
Purchase #7	$244.64	3.430%	$253.0312	$253.03	$253.05	$253.00
7 purchase totals =	$1,073.32		$1,173.8903	$1,173.90	$1,173.90	$1,173.90