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	$205.37	12.747%	$231.5485	$231.55	$231.55	$231.50
Purchase #2	$50.65	8.398%	$54.9036	$54.90	$54.90	$54.90
Purchase #3	$134.29	6.597%	$143.1491	$143.15	$143.15	$143.10
Purchase #4	$121.88	13.671%	$138.5422	$138.54	$138.55	$138.50
Purchase #5	$100.69	12.587%	$113.3639	$113.36	$113.35	$113.40
Purchase #6	$93.96	6.562%	$100.1257	$100.13	$100.15	$100.10
Purchase #7	$101.74	12.853%	$114.8166	$114.82	$114.80	$114.80
7 purchase totals =	$808.58		$896.4496	$896.45	$896.45	$896.30