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	$37.34	4.229%	$38.9191	$38.92	$38.90	$38.90
Purchase #2	$181.64	7.665%	$195.5627	$195.56	$195.55	$195.60
Purchase #3	$157.29	6.522%	$167.5485	$167.55	$167.55	$167.50
Purchase #4	$146.40	12.514%	$164.7205	$164.72	$164.70	$164.70
Purchase #5	$110.55	10.831%	$122.5237	$122.52	$122.50	$122.50
Purchase #6	$13.77	9.785%	$15.1174	$15.12	$15.10	$15.10
Purchase #7	$43.93	3.673%	$45.5435	$45.54	$45.55	$45.50
7 purchase totals =	$690.92		$749.9354	$749.93	$749.85	$749.80