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	$134.55	11.666%	$150.2466	$150.25	$150.25	$150.20
Purchase #2	$138.74	12.402%	$155.9465	$155.95	$155.95	$155.90
Purchase #3	$244.63	11.161%	$271.9332	$271.93	$271.95	$271.90
Purchase #4	$191.74	3.872%	$199.1642	$199.16	$199.15	$199.20
Purchase #5	$97.88	7.789%	$105.5039	$105.50	$105.50	$105.50
Purchase #6	$39.81	9.527%	$43.6027	$43.60	$43.60	$43.60
Purchase #7	$13.91	7.846%	$15.0014	$15.00	$15.00	$15.00
7 purchase totals =	$861.26		$941.3985	$941.39	$941.40	$941.30