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	$38.71	12.381%	$43.5027	$43.50	$43.50	$43.50
Purchase #2	$188.82	4.115%	$196.5899	$196.59	$196.60	$196.60
Purchase #3	$103.80	9.108%	$113.2541	$113.25	$113.25	$113.30
Purchase #4	$84.56	8.169%	$91.4677	$91.47	$91.45	$91.50
Purchase #5	$183.26	12.703%	$206.5395	$206.54	$206.55	$206.50
Purchase #6	$133.76	9.236%	$146.1141	$146.11	$146.10	$146.10
Purchase #7	$80.84	7.475%	$86.8828	$86.88	$86.90	$86.90
7 purchase totals =	$813.75		$884.3508	$884.34	$884.35	$884.40