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	$39.45	7.800%	$42.5271	$42.53	$42.55	$42.50
Purchase #2	$35.65	7.202%	$38.2175	$38.22	$38.20	$38.20
Purchase #3	$84.99	5.320%	$89.5115	$89.51	$89.50	$89.50
Purchase #4	$174.63	3.858%	$181.3672	$181.37	$181.35	$181.40
Purchase #5	$96.52	9.237%	$105.4356	$105.44	$105.45	$105.40
Purchase #6	$43.43	5.499%	$45.8182	$45.82	$45.80	$45.80
Purchase #7	$78.77	4.183%	$82.0649	$82.06	$82.05	$82.10
7 purchase totals =	$553.44		$584.9420	$584.95	$584.90	$584.90