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	$88.40	13.271%	$100.1316	$100.13	$100.15	$100.10
Purchase #2	$190.63	5.233%	$200.6057	$200.61	$200.60	$200.60
Purchase #3	$52.65	13.116%	$59.5556	$59.56	$59.55	$59.60
Purchase #4	$102.78	10.815%	$113.8957	$113.90	$113.90	$113.90
Purchase #5	$41.69	3.292%	$43.0624	$43.06	$43.05	$43.10
Purchase #6	$42.95	10.290%	$47.3696	$47.37	$47.35	$47.40
Purchase #7	$62.57	9.590%	$68.5705	$68.57	$68.55	$68.60
7 purchase totals =	$581.67		$633.1911	$633.20	$633.15	$633.30